ELEMENTS (Nonmetals) CARBON(C) - The...
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1 ELEMENTS (Nonmetals) CARBON(C) Whenever we think of carbon, something black comes to your mind, because carbon is black. This is not entirely true. What we see black is coal or charcoal or coke which are the common forms called allotropes of carbon. Not all forms of carbon are black. The element, carbon exists in different physical forms called allotropes. Diamond, which is so beautiful and glittering is nothing but a form of carbon( 6 C 12 ). It is not black, it is a multifaceted stone. Graphite which is used as the pencil lead (don't mistake this lead with the metal lead, Pb) is another allotrope of carbon. This has a shining lustre like a metal, and has a greyish white colour. Carbon is present in hundreds and thousands of compounds those are found in plants and animals. The proteins, carbohydrates, fats, vitamins and a large number of compounds found in living beings contain carbon as one of the elements. In fact the very existence of life force on earth is due to carbon compounds. Such is the importance of carbon, which, as an element in the form of coal is so much disliked as it looks pitch black. In fact the number of carbon compounds is so large and unlimited that a separate branch called organic chemistry deals with them. We shall study about organic chemistry in some details in the last section of this book. Many inorganic minerals like CaCO 3 , MgCO 3 etc. found in the earth crust also contain carbon as one element. The atmosphere contains CO 2 gas which contain carbon. Smoke which is a common pollutant in our atmosphere is nothing but carbon particles suspended in air. CO which is another pollutant contains carbon. As element carbon is available in two broad forms: (i) Crystalline (ii) Amorphous Crystalline Forms: You know that crystalline form contains crystal structures of fixed shape and size. In crystals the atoms are arranged in a systematic and orderly manner and repeated with the same pattern throughout. Carbon has three crystalline forms. (a) Diamond (b)Graphite (c)Fullerene DIAMOND: We are very much fond of diamonds because they look so beautiful when used in jewellery. These are very costly shining stones because it is not available in nature abundantly like other forms of carbon. In nature it is produced in igneous rocks below 150km from the earth's surface. It is believed that when molten rocks (mostly magnesium carbonate) at such a depth compress CO 2 gas at a very high pressure and high temperature, crystallization of carbon particles take place there to form this beautiful stonelike form of carbon called diamond. Do you know three special qualities of diamond apart from its use in jewellery? 1. It is the hardest substance known. Could you believe that diamond is even harder than metals. While the ordinary form of carbon such as coal, charcoal etc. are so soft, the diamond is even harder than iron or any metal!! It is really unbelievable. That is why it is used for drilling holes on rocks and sharpening metal tools. Sharpening of a tool is done by continuous rubbing of diamond on the metallic surface of the tool. Due to friction, the surface of the metal erodes and metal is lost as fine powder from the surface. But diamond does not suffer any loss of its substance from the friction surface. Such type of materials are called abrasive. The density of diamond is not much(3.51gm/cc) compared to metals, but its hardness is the greatest!!!
Transcript of ELEMENTS (Nonmetals) CARBON(C) - The...
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ELEMENTS(Nonmetals)
CARBON(C)Whenever we think of carbon, something black comes to your mind, because carbon is black.This is not entirely true. What we see black is coal or charcoal or coke which are the commonforms called allotropes of carbon. Not all forms of carbon are black. The element, carbon existsin different physical forms called allotropes. Diamond, which is so beautiful and glittering isnothing but a form of carbon(
6C12). It is not black, it is a multifaceted stone. Graphite which is
used as the pencil lead (don't mistake this lead with the metal lead, Pb) is another allotrope ofcarbon. This has a shining lustre like a metal, and has a greyish white colour. Carbon is presentin hundreds and thousands of compounds those are found in plants and animals. The proteins,carbohydrates, fats, vitamins and a large number of compounds found in living beings containcarbon as one of the elements. In fact the very existence of life force on earth is due to carboncompounds. Such is the importance of carbon, which, as an element in the form of coal is somuch disliked as it looks pitch black. In fact the number of carbon compounds is so large andunlimited that a separate branch called organic chemistry deals with them. We shall study aboutorganic chemistry in some details in the last section of this book. Many inorganic minerals likeCaCO
3, MgCO
3 etc. found in the earth crust also contain carbon as one element. The atmosphere
contains CO2 gas which contain carbon. Smoke which is a common pollutant in our atmosphere
is nothing but carbon particles suspended in air. CO which is another pollutant contains carbon.As element carbon is available in two broad forms:
(i) Crystalline (ii) AmorphousCrystalline Forms:You know that crystalline form contains crystal structures of fixed shape and size. In crystals theatoms are arranged in a systematic and orderly manner and repeated with the same patternthroughout. Carbon has three crystalline forms.
(a) Diamond (b)Graphite (c)FullereneDIAMOND:We are very much fond of diamonds because they look so beautiful when used in jewellery.These are very costly shining stones because it is not available in nature abundantly like otherforms of carbon. In nature it is produced in igneous rocks below 150km from the earth's surface.It is believed that when molten rocks (mostly magnesium carbonate) at such a depth compressCO
2 gas at a very high pressure and high temperature, crystallization of carbon particles take
place there to form this beautiful stonelike form of carbon called diamond. Do you know threespecial qualities of diamond apart from its use in jewellery?1. It is the hardest substance known.Could you believe that diamond is even harder than metals. While the ordinary form of carbonsuch as coal, charcoal etc. are so soft, the diamond is even harder than iron or any metal!! It isreally unbelievable. That is why it is used for drilling holes on rocks and sharpening metal tools.Sharpening of a tool is done by continuous rubbing of diamond on the metallic surface of the tool.Due to friction, the surface of the metal erodes and metal is lost as fine powder from thesurface. But diamond does not suffer any loss of its substance from the friction surface. Suchtype of materials are called abrasive. The density of diamond is not much(3.51gm/cc) comparedto metals, but its hardness is the greatest!!!
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2. It has the highest melting point of all elements known. Its melting point is unbelievablyhigh (35470C). The boiling point is still higher(48270C).3. It has the highest thermal conductivity:Its thermal conductivity is nearly five times greater than copper. This is indeed unbelievable!!!That means it conducts and dissipates the heat to the greatest extent and does not allow the heatto accumulate on it. This property is best suitable for its use as abrasives (sharpening metaltools) and drilling tool. It does not get heated up by continuous friction with metals or other rocksetc.The cause of such high thermal conductivity exhibited by a nonmetal is not clear.
STRUCTURE OF DIAMOND:Diamond has a unique structure. Carbon atoms in diamond do not exist as free atoms. All theatoms are interconnected and forms an infinite network. Each carbon atom is connected withfour other carbon atoms by covalent bonds in a tetrahedral geometry. If one carbon atom lies at
the centre of the tetrahedron, four other carbon atoms lie at the four corners of that tetrahedron.This structure continues in all directions. Diamond stone is a single giant molecule containinginfinitely large number of carbon atoms connected with each other in a tetrahedral network.It has a infinitely large molecular mass.Properties:1. Diamond is a bad conductor of electricity.
2. Diamond when heated to 9000C, reacts slowly with O2 to form CO
2. But when it is
heated to above 1000C, it changes its physical form to graphite.Its beautiful stonelike appearancevanishes and looks greyish coloured graphite.
GRAPHITE:Graphite is very soft which is opposite in behaviour compared to its crystalline partner, diamond.The pencil lead is made up of graphite. It marks paper and soils fingers when touched. It meansthat a small part of graphite sticks onto our fingers or paper when we rub it on our fingers orpaper. There are two special qualities of graphite.
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1. It is a good conductor of electricity. It is therefore often used to make electrodes tocarry out electrolysis of different electrolytes. Look to its crystalline sister, diamond which is abad conductor. Very interesting indeed!!!2. It is a nonmetal but looks like metal because of its shining lustre.3. It has high thermal conductivity (although less than diamond) equal to that ofaluminium.4. Its mechanical strength increases with increasing temperature. Usually with increaseof temperature the mechanical strength of a material decreases. Graphite behaves just in theopposite way.
STRUCTURE:Graphite has another typical structure. Carbon atoms are arranged in several parallel layersplaced one above the other. The layers are not connected with each other and there is good gapbetween the layers. But in each layer, carbon atoms are connected with each other bycovalent bonds forming a two dimensional hexagonal network. The carbon atoms are sitting
at the vertices of the hexagons. Each carbon atom in a layer is connected with three neighbouringcarbon atoms of the same layer. You know that carbon has four electrons in its valence shell, outof which three are utilized for forming three covalent bonds with three neighbouring atoms. Soone unpaired electron is left out on each carbon atom present in the layer. These form pi(πππππ)bonds(very weak covalent bond) among carbon atoms. Thus there is alternate single bonds anddouble bonds between carbon atoms which are present in each layer. We know from the topic,"chemical bond" that a pi(π) bond alongwith a sigma bond result in a double bond. The pi bondpresent in the double bond is very weak and the electron pair forming it is almost free. Thesebehave like free electrons When a potential difference is applied to graphite at two ends, thesefree electrons drift in one direction being attracted by positive potential and repelled by negativepotential and thus conducts electricity.
These are called free elec
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3. FULLERENE:This is another crystalline form of carbon which has been recently discovered. This looks like afootball having a spheroidal shape. Among fullerenes C-60(called as carbon sixty) is mostimportant and widely studied. There are 60 carbon atoms arranged like a football. This wasdiscovered by R.Curl, H. Croto and R. Smalley in 1985 who got Nobel prize in 1996. This iscalled a Bucky ball as it was named after the Britisch architect engineer, Buckminster Fullerwho first constructed geodesic dome. The bucky ball of fullerene has 20 hexagons and 12pentagons and carbon atoms are present in the sixty vertices having 32 faces. The geometricalshape is called truncated icosahedron. Each hexagon is surrounded by 3 pentagons and 3 hexagonin an alternating manner while each pentagon is surrounded by five hexagons. The 6-6 ring
junction is a C=C double bond while a 5-6 junction is a C–C single bond. Earlier it was believedthat fullerne is a super-aromatic as there are 20 benzene rings in which extensive resonance isoccuring. Later on it was believed that fullerene is a super-alkene as there is limited resonanceand the C=C are almost localised. C-60 fullerene has many versatile applications such assemiconductors, superconductors, in the field of medicine, nanotechnology, catalysis and manyothers.
AMORPHOUS FORMS:Amorphous substances are powdery in nature and the atoms in these substances are not arrangedin an systematic and orderly manner. Coal is the natural amorphous form of carbon. Out ofseveral synthetic amorphous forms charcoal, coke and carbon black are superior forms andare believed to have a small degree of crystallinity. Coal is the most abundant amorphous formof carbon available in the earth crust in coalfiels. The Talcher coal fields in Orissa, Raniganjin West Bengal and so many others in India are some of the places where coal is mined. Coalis primarily used as fuel.COAL:There are four types of coal.1. Peat: It contains the minimum carbon content(4-10%). It is used to make charcoal andin horticulture.2. Lignite : It contains 25-35% of carbon and is called the youngest coal. It is used inthermal power plant.
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3. Bituminous: It contains 45-86% of carbon and is called soft coal. It is used for domesticand industrial fuel and also used to make coke.4. Anthracite: It contains 86-98% carbon and is the purest form of carbon. It burns withblue flame and is used in household fire places.Synthetic Amorphous Carbon:1. Charcoal: It is produced when sugar, wood, blood or other carbon containingsubstances are burnt in limited supply of air. Sugar charcoal is pure. Activated charcoal is usedto adsorb gases, liquids or solids on its surfaces. Activation of charcoal is done by passing steamover passive charcoal which removes all substances adsorbed on the surface of charcoal.2. Coke: When coal is heated in the absence of air(destructive distillation), weget a form of carbon called coke in the residue. Coke is used as a reducing agent to reducemetallic oxides to free metals in metallurgy.3. Carbon Black: This is produced by burning hydrocarbons(such as candle wax, kerosene,petrol, diesel etc) in the limited supply of air. This is used in rubber industries for making tyresand in preparing printing ink and shoe polish.
CHEMICAL PROPERTIES:Carbon has the unique property to form repeated single bonds with itself as given below
C C C C C C
This property of carbon is called CATENATION. No other element shows such a high extent ofcatenation like carbon. This is because the C-C single bond energy is very high. Bond energyis the amount of energy released during the formation of the bond. More the bond energymore is stability of the system.
Some of the chemical properties of carbon are depicted in the form of equations. Every form ofcarbon described above namely coal, coke, charcoal etc. shows these reactions. Assess thelogic of each reaction by yourself.1. C + O
2(sufficient) -------> CO
2(R) Show the changes in ON
C + O2(limited) ----------> CO (R) show the changes in ON
2. +++ CO 2 SO2 H2O(conc.)C H2SO4 (R) (refer the topic H2SO
4)
3. +++ CO2 NO2 H2O(conc.)C HNO3 (R) (refer the topic HNO3)
4. C(red hot) + H2O(steam) ---------> CO + H
2(R) (show the changes in ON)
The mixture of CO and H2 is called the water gas.
5.+20+20
Pb CO++C PbO
Thus carbon reduces many metallic oxides to their corresponding metals. This is used in theextraction of metals in the metallurgy.
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HYDROGEN (H2)
You know hydrogen is the first element in the periodic table and is a diatomic gas which is itselfcombustible. It is therefore dangerous to handle hydrogen gas because it catches fire. In balloonswe fill H
2 gas as it is the lightest element. Hydrogen occurs mainly in water and in organic
substances along with carbon. It is colourless, odourless and tasteless gas.
ISOTOPES AND NUCLEAR ISOMERSHydrogen exists as three isotopes, namely (i)protium, (
1H1)also calld hydrogen, (ii)deuterium(
1D2
or 1H2), (iii)Tritium (
1T3 or
1H3). In nature, the deuterium is present in very small quantities
(0.02%) and tritium is almost absent. Tritium is now produced by artificial methods.Hydrogenalso exists as two nuclear isomers, namely ortho hydrogen and para hydrogen. If thenuclei(protons) of the two H atoms in H
2 molecule spin in the same direction, it is called ortho-
H2 and if the nuclei spin in opposite direction, it is called para-H
2.
PREPARATION:1. Metals lying above H in the electrochemical series displace H
2 from dilute acids.
Zn + HCl(dil.) -------:> ZnCl2 + H
2, Al + H
2SO
4 ------> Al
2(SO
4)
3 + H
2 and so on.
These are all redox reaction and the sub-type is displacement reaction (refer section-I).Showthe changes in ON in each reaction.2. Displacement of H
2 from water by very active metals:
Very active metals like Li, Na,K, Ca etc. displace water from cold water, metal like Mg displacesH
2 from boiled water, and metal like iron displace H
2 from water under more vigorous conditions.
Look to these reactions.Na + H
2O -------> NaOH + H
2, Ca + H
2O ------> Ca(OH)
2 + H
2
Mg + H2O(boiled)-------> MgO + H
2
Fe(red hot) + H2O(steam)------> Fe
3O
4(magnetic oxide) + H
2
Show the changes in ON in each equation and balance them. These are all redox reactions.Wealready know them in section-I.3. Amphoterism:Metals like Zn, Al, Sn, Pb, Si etc(see section-I) react with strong base like NaOH or KOHproducing H
2 gas. This is redox(amphoterism) type of reaction.
Zn + NaOH ------> Na2ZnO
2 + H
2, Al + KOH -------> KAlO
2 + H
2
Show the changes in ON.4. Electrolysis of water:We know from the chapter, electrochemistry that pure water is a bad conductor of electricitybut if there is a soluble electrolyte like acid or NaCl in it, it conducts electricity. Electrolysis ofsuch solution produces H
2 at cathode and O
2 at anode.
PROPERTIES:Some of the important chemical reactions are listed below. Study the logic of each.1. H
2 + O
2 -------------> H
2O (R)
At ordinary conditions, the reaction is so slow that virtually it does not take place. However if anelectric spark is introduced into a mixture of H
2 and O
2, a pop sound is heard and we get water
instantly.
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2. H2 reduces many metallic oxides.
CuO + H2 -------> Cu + H
2O (R) Show the changes in ON.
3. With various nonmetals H2 forms their hydrides.
H2 + Cl
2 -----> HCl, H
2 + S -----> H
2S, H
2 + N
2 ------> NH
3 and so
on.Each is a redox reaction under the type synthesis. Show the changes in ON in each case.4. With alkali and alkaline earth metals, H
2 forms their hydrides.
Na + H2 -------> NaH, Ca + H
2 -------> CaH
2
These are redox reactions of the type synthesis. Show the changes in ON in each.The metallic hydrides are very reactive compounds and produce H
2 gas when react with H
2O.
+ +0
NaH H2O NaOH H2
-1 +1
(R)
Here H is oxidised from -1(NaH) to 0(H2) and same H is reduced from +1(H
2O) to 0(H
2).
USES:1 Used in rockets as fuel. 2. Used in the synthesis of ammonia(Haber'sprocess) 3. Used for hydrogenation of oil: vegetable oil is converted to solid fat bythis way.4. Used to make oxyhydrogen flame to produce very high temperature.
SULPHURDo you know that sulphur has another very old English name known as "brimstone", whichmeans stone that burns. Sulphur is available in the free state underground as a brittle yellowstone which burns with a beautiful blue flame. Free sulphur is also available near volcanoes andhot springs. It is also available in combined form in many minerals. It is present also in plants andanimals and substances such as mustard, garlic, cabbage, wool and hair.Free sulphur is mined from underground by Frasch's process. The process is very simple. Themelting point of sulphur is 1130C. Compressed steam whose temperature is higher than 1130C ispumped inside earth through a vertical pipe extending upto underground sulphur bed. The sulphurmelts and molten sulphur is pumped out by forcing compressed air inside.PROPERTIES:Allotropes of Sulphur:Sulphur in the solid state remains in many physical forms(allotropes) such as
1. Rhombic Sulphur: This is a crystalline form of sulphur. Below 95.50C, sulphurremains in this form. This the most stable form of sulphur and is lemon yellow in colour. It isinsoluble in water but highly soluble in CS
2 which is a non-polar solvent. Could you know the
reason? The answer is- like dissolves like(Refer chapter, chemical bond). It consists of S8
molecules (not atoms) in which eight atoms are connected by covalent bonds in a crown likeshape.
8
S
S
S
S
S
S
S
S
2. Monoclinic(Prismatic) Sulphur: Above 95.50C, sulphur remains in this form. This existsas very narrow needle shaped and straw brown coloured crystals. It also consists of S
8 molecules
like rhombic form. It is lighter than rhombic form and insoluble in water while soluble in CS2.
3. Plastic Sulphur: This is the amorphous form of sulphur, which behaves like arubber. When liquid sulphur is heated near its boiling point(4440C) and is suddenly put in coldwater, we get this plastic sulphur. This consists of long chain of sulphur atoms, nearly 3,00,000 ofS atoms connected by covalent bonds. This long chain is called a polymer chain. The sulphurremains in this form for a limited time period. Slowly the plastic sulphur changes to rhombic formon standing.4. Milk of Sulphur: When H
2S gas is bubbled through aqueous solution of SO
2, we get
sulphur in the form of yellowish white suspension. The precipitate does not separate out butappear as cloudy milk-like suspension. This is called milk of sulphur. When a thiosulphate salt istreated with a mineral acid, we get sulphur in the form of milk of sulphur alongwith SO
2 gas
which is evolved.0+4+2
+++ Na2SO4 SO2 S(milk of sulphur)Na2S2O3 H2SO4(dil)
Now let us know something about the liquid state of sulphur.LIQUID SULPHUR:When sulphur melts to a yellow liquid at 1130C it changes into a free flowing liquid like water.But when the temperature is raised gradually, colour slowly changes to dark red at 2000C and itsviscosity increases and liquid becomes thicker like oil. Above 2000C, the viscosity decreases andgradually the intense colour also fades. Do you guess the reason? Upto 2000C, the S
8 rings open
up and join in straight chain to form long chain molecules. As the length of the chain goes onincreasing, they entangle(knot) each other and viscosity increases. Above 2000C, the S-S bondsstart to break and length of chain starts decreasing. So the viscosity again decreases.
S8 + S
8 + S
8 ...... --------------> .....S-S-S-S-S-S....... upto 3,00,000 atoms(polymer
chain)
CHEMICAL PROPERTIES:Sulphur, although a nonmetal, is very reactive. It shows oxidation numbers from -2 to +6. Itreacts with most of the metals and nonmetals. Some of the reactions are given below. Study thelogic of each reaction. For equations, knowingly we don't write S
8 rather we write S to avoid
complexity in balancing.1. Synthesis reactions:
Mg +S ------> MgS, S + F2 ------> SF
6( s u l p h u r
hexafluoride)C + S -------> CS
2 (a solvent) S + O
2 ------> SO
2. This is the burning reaction.
S + Cl2 -------> S
2Cl
2(sulphur monochloride)
All these are redox reaction of the type-synthesis. Find the changes in ON in each case.
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2. With strong oxidising acids: We know the reaction of S with conc. H2SO
4 and conc.
HNO3 before. Try to practise these again now.
3. With conc. alkalis: When S is heated in an alkali(say NaOH), disproportionation(redox) reaction takes place. S is oxidised to SO
32- and also is reduced to S2-.
-2
Na2SO3 Na2S H2ONaOH S 0 +4
+++ (Redox: disproportionation)
Sulphite salts when react with excess of sulphur to produce thiosulphate. See below.
Na2S2O3Na2SO 3 S0+4 +2
+ (R)
Here S is reduced from +4(Na2SO
3) to +2(Na
2S
2O
3) while the same S is oxidised from 0 to
+2(S2O
32-).
USES:1. Used to harden rubber in the process called vulcanization of rubber.2. Used to produce SO
2 which is used to manufacture H
2SO
4.
3. Used in drugs and dyes, fertilizers.
CHLORINE(Cl2):
Do you know that the diatomic gas chlorine is a poisonous gas which can affect the lungsseverely and for this reason it was used as a war gas in world war I? The Greek word "Chloros"means greenish yellow which is the colour of chlorine. It is not available in free state but in thecombined state present in many minerals, the most common and abundant among them is sodiumchloride.PREPARATION:1. From hydrochloric acid(HCl):Strong oxidising agents like manganese dioxide(MnO
2), lead dioxide(PbO
2), red led(Pb
3O
4),
potassium permanganate, ozone(O3) etc. can oxidise hydrochloric acid to Cl
2 gas. Look to the
following reactions and study their logic. The reactions are not balanced. Balance them by eitherON method or partial equation method. Refer section-I, if necessary. In all these reactions HClis oxidised to Cl
2.
++++2 0-1+4
MnCl2 Cl2 H2OMnO2 HCl ,
PbO 2 HCl PbCl2 Cl2 H2O+4 -1 0+2
+ + +
++++2 0-1PbCl2 Cl2 H2OPb3O4 HCl +++
+83
,
0-1
O3 HCl O2 Cl2 H2O-20
+ ++
Note that in all the reactions of ozone, we get oxygen gas along with other products due tooxidation and reduction. Refer the topic ozone for that.
+2
KMnO4 HCl (conc.) KCl MnCl2 Cl2 H2O+7 -1 0
+ + + +
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The pink colour of KMnO4 becomes colourless(MnCl
2) In the laboratory, usually Cl
2 gas is
prepared from MnO2 or KMnO
4 as shown above. The gas is passed through water to remove
the impurity HCl gas which is absorbed by water and then through conc. H2SO
4 to remove
moisture. The dried gas is then collected by upward displacement of air as it is heavier than air.
2. From Bleaching powder:Bleaching powder, which is commonly written as Ca(OCl)Cl reacts with dilute mineral acids likeH
2SO
4, HCl and acidic oxide like CO
2 to produce Cl
2 gas.
Ca(OCl)Cl H2SO4(dil.) CaSO4 Cl2 H2O+1 0-1
+ ++
Ca(OCl)Cl HCl(dil.) CaCl2 Cl2 H2O+1 0-1
+ ++ ,
Ca(OCl)Cl CO2 CaCO3 Cl2 +1 0-1
++
Note that bleaching powder contain two acid radicals, hypochlorite in which the ON of Cl is +1and chloride in which the ON of Cl is -1. This reaction is a disproportionation (redox) reactionin which the ON of Cl is increased from -1 to 0(oxidation) and decreased from +1 to 0(reduction).This is brought about in presence of a mineral acid. CO
2 is the anhydride of H
2CO
3, so carbonate
salt is formed.
PROPERTIES:It is moderately soluble in water and gives the solution called chlorine water, which is a goodoxidising agent.
Cl2 + H
2O --------> HCl + HClO,
It forms hydrochloric acid and hypochlorous acid when dissolved in water. But when it reacts asan oxidising agent it breaks like this.
Cl2 + H
2O -------> 2 HCl + [O],
the nascent oxygen oxidises the reducing agent.1. As Oxidising Agent:Whether in the form of Cl
2 gas or Cl
2 water, it is a good oxidising agent and in all the cases, it is
reduced to HCl. The ON changes from 0 to -1. Some of the oxidising actions are depictedbelow. Study them.(i) With ammonia: Refer the chapter NH
3 for this.
(ii) With bromide, iodide salts:Since Cl lies below Br and I in the electrochemical series and is more easily reduced from Cl
2 to
Cl- compared to Br2 and I
2 reduced to Br - and I- respectively. So Cl
2 is the most active halogen
among the three(but less than F2) and is better oxidising agent than Br
2 and I
2 and can displace
Br2 and I
2 from the bromide and iodide salts respectively. However, Br
2 and I
2 cannot displace
Cl2 from chloride salts.
Cl2 KBr KCl Br2+ +0 -1-1 0
, Cl2 KI KCl I2+ +0 -1-1 0
(iii) With reducing agents like H2S, FeCl
2, acidified FeSO
4, Na
2SO
3, SO
2, Na
2S
2O
3.
H2S gives yellowish white sulphur suspension, green FeCl
2 is changed to reddish brown FeCl
3,
green FeSO4 is changed to reddish brown Fe
2(SO
4)
3; Na
2SO
3 forms Na
2SO
4; SO
2 is oxidised
to H2SO
4 while Na
2S
2O
3 is oxidised to Na
2SO
4. In all these cases Cl
2 is reduced to HCl. Study
their logic.
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+H2S Cl2 S HCl-2
+00 -1
, FeCl2 Cl2 FeCl3++3+2 0 -1
Cl2 FeSO4 H2SO4 HCl Fe2(SO4)3 ++ ++2 +30 -1
Cl2 Na2SO3 H2O HCl Na2SO4 +6+40 -1
+++ ,
+6Cl2 H2O SO2 HCl H2SO 4++ +0 +4 -1
+2Na2S2O3 Cl2 H2O Na2SO4 HCl S + +++
+60 -1 0
In the last three reactions, we have to take H2O, otherwise we cannot balance the equations. In
the other reactions, we do not require H2O in the reaction, even though it might be carried out in
water medium. Note that in most of the reactions involving thiosulphate, S is produced alongwithother products.2. Disproportionation(redox) reactions:(i) With alkalis:Alkalis like NaOH, Ca(OH)
2 react with Cl
2 in two conditions, (a)cold and dilute alkali with Cl
2,
(b)hot and concentrated alkali with Cl2. In all these reactions, Cl gets oxidised as well as reduced.
Hence these are disproportionation reactions(refer section-I).(a) Cold and dilute alkali: In this case chloride and hypochlorite salts are produced.
NaOH Cl2 NaOCl NaCl H2O+ ++0 +1 -1
Ca(OH)2 Cl2 Ca(OCl)2 CaCl2 H2O+ ++0 +1 -1
(b) Hot and concentrated alkali: In this case chloride and chlorate are formed.-10
+ ++NaClO3 NaCl H2ONaOH Cl2+5
-10+ + +Ca(ClO)3 CaCl2 H2OCa(OH)2 Cl2
+5
(ii) Preparation of Bleaching powder from dry slaked lime:Dry Cl
2 reacts with dry slaked lime(calcium hydroxide) to form bleaching powder.
Cl2 Ca(OH)2 Ca(OCl)Cl H2O++0 +1 -1
,
In this case, both hypochlorite and chloride are present in the same compound sometimes calledcalcium oxychloride(bleaching powder). Note that if the reaction is carried out in water, bleachingpowder is not formed. Chlorate and chloride are obtained as discussed before.3. Addition reactions: (Redox)
Cl2 reacts with many metals, nonmetals and compounds to give addition products. All
these are redox reactions.H
2 + Cl
2 ---light-----> HCl (R) Show the changes in ON yourself.
P4 +Cl
2 ----------> PCl
3(R) P from 0 to +3, Cl from 0 to -1
P4 + Cl
2(excess) -----> PCl
5(R), P from 0 to +5 and Cl from 0 to -1
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Na + Cl2 --------> NaCl (R) Find the change in ON yourself
Al + Cl2 -------> AlCl
3(R) Show the changes in ON.
SO2 + Cl
2 -------> SO
2Cl
2(sulphuryl chloride) (R)
Here the ON of S changes from +4 to +6 and that of Cl reduced from 0 to -1.CO + Cl
2 -------> COCl
2 (carbonyl chloride or phosgene) (R)
Here the ON of C changes from +2 to +4 while that of Cl from 0 to -1.USES:1. As a bleaching agent(that which removes colour) for cotton fabric, paper etc.2. For killing germs in drinking water(disinfectant).3. For manufacture of bleaching powder and hundreds of other chemicals.
OXYGEN(O2):
The diatomic gas O2 is the key to life force on earth used in respiration of plants and animals. All
burning(combustion) processes occur only with the help of oxygen. Our atmosphere containsnearly 21% of O
2 gas. It occurs in the combined state abundantly in different types of
clays(silicates), sand (silicon dioxide), oxides of metals and in water. It has three naturally occurringisotopes, O16, O17 and O18 out of which O16 constitutes nearly 99.8%. Oxygen gas is prepared inlarge scale from air. First air is liquified and then the two major constituents present in it namelyO
2 and N
2 are separated by fractional distillation as the boiling points of liquid O
2 and N
2 are
different.
PREPARATION:1. From Potassium Chlorate:When heated, postassium chlorate decomposes to give O
2. If a small amount of MnO
2 is added
in KClO3, the O
2 is evolved at a faster rate. MnO
2 acts as a catalyst in this reaction. You know
that catalysts are usually the substances which enhance the rate of a reaction, without themselvesundergoing any change.The reaction is a disproportionation type under the category of redoxreaction. The same substance gets oxidised and reduced. Check this from the equation.
MnO2-2 0-1+5
+KCl O2KClO3 (R) Balance this equation.
2. From Unstable Metallic Oxides:Oxides of metals like Hg and Ag are unstable. On heating, they decompose to produce O
2 gas
and the corresponding metal. In fact, O2 gas was discovered by Pristley by heating mercuric
oxide(HgO).0-2 0+2
+Hg O2HgO (R),+1 0-2 0
+Ag O2Ag2O (R)
These are also disporportionation reactions.3. By Heating Some Higher Oxides:Some higher oxides on heating change to oxides in their lower oxidation states while liberatingO
2 gas.
0-2 +238+
+PbO O2Pb3O4 , (R),+4 0-2 +2
+PbO O2PbO2 (R)
13
In each case you find that O is oxidised from -2 to 0 and metal is reduced from higher state to +2state.4. Decomposition of oxygen containing compounds:Compounds like nitrates, KMnO
4, K
2Cr
2O
7 on strong heating give O
2. Study each reaction and
balance them. All are disproportionation reactions under the redox category.0-2 +3+5
+NaNO2 O2NaNO3 (R),0-2 +3+5
+KNO2 O2KNO3 (R)
Nitrates of other metals give reddish brown nitrogen dioxide(NO2) gas along with O
2 gas. This
method is not therefore used to prepare O2 gas. Let us see one such reaction.
0-2 +4+5++CuO NO2 O2Cu(NO3)2 (R)
Note that nitrates of Na and K give O2 and their nitrite salts, while the nitrates of all other metals
give oxides of the metals(not their nitrites).0+4-2 +6+7
++K2MnO4 MnO2 O2KMnO4 (R) Balance the reaction.
0-2 +3+6
++K2CrO4 Cr2O3 O2K2Cr2O7 (R) Balance the
reaction.5. Decomposition of Peroxides:Hydrogen peroxide, sodium peroxide, barium peroxide etc. on heating produces O
2 gas alongwith
oxides of the elements. These are also disproportionation reactions.-2-1 0
+H2O O2H2O2 (R),
This reaction is catalysed by a small quantity of MnO2, Pt etc.
-2-1 0+Na2O O2Na2O2 (R),
-2-1 0+BaO O2BaO2 (R)
PROPERTIES:It is a colourless, odourless and tasteless gas. Although the gas is colourless, liquid oxygen(boilingpoint -1830C) is pale blue in colour. It is not combustible gas like H
2. But it supports the combustion
of all substances. It is the second most electronegative element(next to F) and is very reactive.It reacts with most metals and nonmetals to produce their oxides.1. Formation of Oxides:Metals form metallic or amphoteric oxides while nonmetals form acidic oxides. All these areredox reactions.
Na + O2 -------> Na
2O and Na
2O
2
(Na from 0 to +1, O from 0 to -2 in oxide and -1 in peroxide)Sodium forms a mixture of oxide and peroxide.Ca + O
2 ------> CaO (Ca from 0 to +2, O from 0 to -2)
Al + O2 -------> Al
2O
3(Al from 0 to +3, O from 0 to -2)
You know that Al2O
3 among the above is amphoteric while all other oxides are metallic. If you
want to know the examples of other amphoteric oxides, then refer amphoterism in section-I.S + O
2 ------> SO
2(S from 0 to +4, O from 0 to -
14
2)C + O
2 -----> CO
2(C from 0 to +4, O from 0 to -2)
P4 + O
2 ------> P
2O
3 or more correctly P
4O
6(P from 0 to +3, O from 0 to -2)
P4 + O
2(excess) -------> P
2O
5 or more correctly P
4O
10(P from 0 to +5, O from 0 to -2)
2. Reaction with NH3: Refer the topic NH
3
USES:1. Used in respiration. 2. Used in metallurgical operations during roasting of ores,refining of metals etc.
OZONE(O3)
Ozone is an allotrope of oxygen. It is not present in our atmosphere. It is present about 20kmabove the ground in the region called stratosphere. This is called ozone layer. God has madeozone, perhaps, to protect us from the harmful effects of ultraviolet radiation that come from thesun. Ozone absorbs all the ultraviolet radiation coming from the sun in stratosphere and preventsits coming to our atmosphere where we live in. However, the ozone in the stratosphere isconstantly being destroyed by the presence of nitric oxide gas which is produced by the supersonicaircrafts, chlorofluorocarbons (CFCl
3 and CF
2Cl
2) which are used in our refrigerators and let
loose to atmosphere. These harmful gases go up to the stratosphere and destroy ozone. Thisdestruction of ozone in the ozone layer is said to produce hole in the ozone layer. For this reason,our earth is in great danger. The plant and animal lives are under great threat due to ultravioletradiation falling on them. Ultraviolet light can cause skin cancer to human beings and do extensivedamage onto the plant life. Therefore, efforts are underway to protect this ozone layer fromfurther destruction.Ozone is a pale blue gas unlike oxygen which is colourless. It has relatively higher boiling point(-1120C) and the liquid ozone is dark blue in colour. It is a V-shaped molecule having bond angleof 116.80.
PREPARATION :Oxygen gas is converted to ozone, by passing oxygen gas through an electric field produced bya high voltage alternating current. This is called silent electric discharge. The O
2 gas is merely
allowed to passed through a tube which is subjected to a high voltage alternating current. This isthe silent discharge. A violent discharge is a sparking process which is not required here. O
2 gas
breaks into O atoms which recombine to produce O3. The instrument in which the conversion of
O2 to O
3 is made is called an ozoniser. In the ozoniser, O
2 gas is partially converted to ozone and
the mixture coming out of the ozoniser is called ozonised oxygen which contains a mixture ofozone and unreacted oxygen. The mixture is cooled to -1120C(boiling point of O
3), at which
ozone separates as a dark blue liquid. O2 does not separate as its boiling point is much lower
(-1830C).PROPERTIES:1. Decomposition:
O3 -------> O
2.
Ozone is decomposed to O2 by the action of heat or ultraviolet light. Catalysts like MnO
2, Pt
etc. enhances the rate of decomposition.
15
2. As an Oxidising Agent:Ozone is a powerful oxidising agent which is more powerful than O
2 gas. In almost all of its
reactions, it gives O2 gas as an additional product. It breaks down into O
2 gas and nascent
oxygen atom. The nascent oxygen atom, in fact, oxidises the reducing agent. Look to the followingreactions. Study the logic of each reaction.(a) With PbS: The black PbS turns to white PbSO
4. In the same manner CuS, ZnS and CdS
are oxidised to their sulphates.
-20 +6-2++ 44 O2 PbSO4 O3 PbS
X 44 PbSO4+PbS [O]
+O2 [O]O3
Note that O2 is produced as an additional product. In all the reactions given below, we shall write
the overall equations, and the reader is advised to balance each equation by partial equationmethod as explained above.(b) With Hg: Mercury is oxidised to mercurous oxide
Hg + O3 -------> Hg
2O + O
2(R), (Hg from 0 to +1 and O from 0 to -2)
Hg2O oxide formed dissolves in mercury and thickens the upper surface of the liquid
mercury in contact with ozone gas. The typical convex meniscus of liquid mercury vanishes dueto that. This is called tailing of mercury.(c) With acidified FeSO
4: Green colour of FeSO
4 changes to reddish brown of Fe
2(SO
4)
3.
FeSO4 + H
2SO
4 + O
3 --------> Fe
2(SO
4)
3 + O
2 + H
2O (R)
(Fe from +2 to +3 and O from 0 to -2)(d) With KI or HI: Ozone oxidises iodide to iodine.
O3 + KI + H
2O --------> O
2 + KOH + I
2(I from -1 to 0 and O from 0 to -2)
(e) With HCl and HBr: Ozone oxidises HCl, HBr to Cl2 and Br
2 respectively.
O3 + HCl ----> O
2 + Cl
2 + H
2O (Cl from -1 to 0 and O from 0 to -2)
O3 + HBr -----> O
2 + Br
2 + H
2O (same as above)
(f) With H2S: Ozone oxidises H
2S to S.
O3 + H
2S ------> O
2 + S + H
2O (S from -2 to 0 and O from 0 to -2)
(g) With Potassium Ferrocyanide:It oxidises potassium ferrocyanide to potassim ferricyanideO
3 + K
4[Fe(CN)
6] + H
2O ------> O
2 + K
3[Fe(CN)
6] + KOH (R)
(Fe from +2 to +3 and O from 0 to -2)(h) With nonmetals: Non metals like I
2, S and P
4 are oxidised to HIO
3, H
2SO
4 and
H3PO
4respectively.
0 -2+5055 2+++ O2 HIO3O3 I2 H2O
X 5+
25
+
+
HIO3I2O5 H2O
I2O5I2 [O]O2 [O]O3
Balancing of the equation is shown by partial equation method. I2 is first oxidised to its stable
oxide (iodine pentoxide), which reacts with water to give its corresponding acid(iodic acid). The
16
reactions with S and P4 are given without balancing. You are advised to balance yourself. S will
first be oxidised to SO3 which will react with H
2O to form H
2SO
4. Similarly P
4 first will give
P2O
5 which will react with H
2O to give H
3PO
4.
-20 0 +6+++ O2 H2SO 4O3 S H2O
+5-20 0+++ O2 H3PO4O3 P4 H2O
USES:1. Ozone is a good bleaching agent. It bleaches oil, delicate fabrics permanently unlikeSO
2. Its bleaching action is due to its oxidising property.
2. As a disinfectant and germicide(killer of germs) in sterilising water.3. As an absorber of harmful ultraviolet light in the stratosphere.
NITROGEN(N2):
The diatomic gas N2 is the essential constituent of air(78% by volume). It is also present in
minerals like Chile salt peter(NaNO3), Indian salt peter(KNO
3). It is also the essential constituent
of proteins found in animals and plants. It is a colourless, odourless, tasteless and non-poinsonousgas.PREPARATION:1. Decomposition of Ammonium Nitrite:NH
4NO
2 on heating gives N
2 and H
2O and leaves no residue.
0+3-32+N2 H2ONH4NO2 (R) Disproportionation
ReactionIt has been discussed in section-I that for ammonium nitrite, remove maximum number of H
2O
molecules from it, the residual gas is N2. Therefore, the coefficient 2 has been written in the
above equation. Note that in stead of taking ammonium nitrite, if a mixture of NaNO2 and
NH4Cl is heated, we also get N
2. This is because first the two react in a metathesis(double
replacement) reaction to give NH4NO
2 which then decomposes in a redox reaction to give N
2.
NH4Cl + NaNO
2 ---heat----> NH
4NO
2 + NaCl (M)
NH4NO
2 -----heat-----> N
2 + 2H
2O (R) as shown above.
2. Decomposition of Ammonium dichromate:Ammonium dichromate on heating produces N
2 gas. This reaction is very interesting. Students
make artificial volcano with the help of this reaction. When heated, the red ammoniumdichromate gives green Cr
2O
3, water and nitrogen gas coming out from the reactant vessel(kept
hidden inside a mountain like dummy) like lava in volcanic eruption!!0 +3+6-3
++N2 Cr2O 3 H2O(NH4)2Cr2O 7 (R)
3. From Ammonia:NH
3 + O
2 --------> N
2 + H
2O (R),
N from -3 to 0 and O from 0 to -2. This reaction is also discussed in the topic NH3.
17
4. From Air:By fractional distillation of liquid air, N
2 is obtained first as the more volatile component when it
is evaporated. Note that the boiling point of N2 is -195.80C while that of O
2 is -1830C. So N
2 is
distilled off first from liquid air.PROPERTIES:Ordinarily N
2 is very inert and does not react with any substance at room temperature. This is
because there is triple bond between the two N atoms which is very strong(Refer the chapterchemical bond).1. With O
2: Nitrogen reacts with O
2 rapidly when electric spark is applied on a
mixture of N2 and O
2 to produce nitrogen monoxide( or nitric oxide, NO). As a matter of fact,
NO is produced in atmosphere by the action of lightening on the mixture of N2 and O
2 present in
air.
+electric spark NON2 O2 (R) Find the change in ON
2. With H2(Haber's process): The manufacture of NH
3 is made from N
2 and H
2(refer
the topic ammonia for details).2. Metals like Li, Mg, Al etc. react with N
2 at high temperature giving metal nitrides.
Li + N2 -------> Li
3N, Mg + N
2 --------> Mg
3N
2
Al + N2 --------> AlN B + N
2 -----------> BN and so on
All these are redox reactions. Try to find the changes in ON in these cases.Note that exceptingLi, no other alkali metal reacts with N
2. All alkaline earth metals react with N
2. Even nonmetal
like B, Si reacts with N2 at high temperature giving their nitrides.
USES:1. Used to fill electric bulb as it is inert and does not react with the filament of the bulb evenat high temperature.2. Used to provide inert atmosphere in many chemical reactions.
PHOSPHOROUS (P4)
Do you know phosphorous glows in dark. It bursts into flame in warm air. You will be surprisedto believe how this element was discovered by Henning Brand. He boiled human urine to get asolid residue and then distilled that residue and got a substance which glowed in dark and burstinto flames in air. This new element was named as phosphorous which in Greek means "bearerof light". From the element phosphorous, the word phosphorescence has been coined. It is thephenomenon in which a material gives off light which it had absorbed before. Like nitrogen,phosphorous is an element essential to life. Our bone contain 20% of phosphorous in the form ofcalcium phosphate. Our teeth are made of calcium phosphate. The DNA which is present in thechromosome of cells contains phosphate. You know DNA controls the genetic make-up(heredity)of plants and animals. The energy produced in the living cells are stored in phosphate calledATP.Phosphorous is available in nature also in minerals called rock phosphate[Ca
3(PO
4)
2]
EXTRACTION OF PHOSPHOROUS:A mixture of rock phosphate, sand(SiO
2) and coke(C) is heated in a furnace at 15000C. In the
first step, calcium phosphate reacts with silica to produce phosphorous pentoxide(P2O
5) and in
the second step, P2O
5 reacts with C and is reduced to P
4. Study the reactions.
18
I. Ca3(PO
4)
2 + SiO
2 ----------> CaSiO
3 + P
2O
5(M)
(Note that the actual formula of phosphorous pentoxide is P4O
10, but we shall write P
2O
5 for
simplicity)This is a metathesis reaction which involved no change in ON of any element.
II. + +0+5 +20P4 COP2O5 C
Phosphorous vapours are distilled out of the furnace with a current of CO2(as it reacts violently
in air/O2) and is condensed under water. Due to its violent reaction in air(O
2), it is stored
under water.PROPERTIES:Allotropes of Phosphorous:There are two main allotropes(physical forms) of phosphorous,
(i)white phosphorous, (ii)red phosphorousWhile the first one i.e the white phosphorous is very reactive and burns spontaneously in warmair, the second one, i.e the red variety is less reactive and catches fire only at 2600C.(i) White Phosphorous:White Phosphorous is a soft and waxy solid, has garlic like smell and contain P
4 molecules. It is
the ordinary form of phosphorous with which we are familiar. Persons working with phosphorousdevelop a disease called, phossy jaw, in which the jaw bones decay. It melts at 440C, highly toxicand has a lower density(1.8gm/cc) than red form(2.3gm/cc). In each P
4 molecule, the four P
atoms are covalently bonded and occupy at four apices(cornors) of a tetrahedron. Its shape istetrahedral. In CH
4(methane), the carbon atom is at the centre of the tetrahedron and the four
C-H bonds are directed towards the four corners of the tetrahedron. But in P4, there is no atom
at the centre of the tetrahedron. The edges of the tetrahedron are the covalent bonds between Patoms. In CH
4, the edges of the tetrahedrons are not bonds, they are the outlines. The bond
angle in P4 is 600 while that in CH
4 109028'. Between P
4 molecules the intermolecular forces are
very weak(Vanderwaals or London forces between non-polar molecules). White phosphorousslowly changes to red form on standing for long years. However on heating white phosphorousto 4000C, it changes rapidly to red form. White phosphorous is soluble in CCl
4 but insoluble in
water.Difference between CH
4 and P
4:
P4:
P P
P
P
600
CH4:
109.50
H
H H
H
C
(ii) Red Phosphorous:It is the stable variety of phosphorous which is nonpoisonous. It does not glow in dark and catchfire under normal conditions. It burns only at a high temperature of 2900C. When its vapours arecondensed, it forms white phosphorous. In red form, the P atoms form long polymeric chain. P
4
tetrahedra are connected with each other to form a long chain like structure in the red form.
19
P4 P4 P4
PROPERTIES:White phosphorous reacts vigorously in all chemical reactions. So we shall discuss the propertiesof white phosphorous.1. With O
2(air): It catches fire in warm air(350C)giving dense white fumes of
phosphorous pentoxide(P2O
5 or P
4O
10).
-20 +5
+ P2O5 (or P4O10)P4 O2 (R)
2. With Cl2: It forms PCl
3 and PCl
5 depending on the amount of Cl
2.
P4 + Cl
2 --------> PCl
3, P
4 + Cl
2(excess) ------.> PCl
5(R)
In the first case, P changes from 0 to +3 and second case from 0 to +5 and in both the cases Clchanges from 0 to -1.3. With Metals: Metals like Mg, Ca etc. react with P
4 to form their phosphides.
Mg + P4 --------> Mg
3P
2(R) Mg from 0 to +2, P from 0 to -3.
4. With strong alkali: When reacts with strong alkali like NaOH or KOH, it producesphosphine(PH
3) gas.
+1-3++ PH3 NaH2PO2(sodium hypophosphite)P4 NaOH
0
This is a disproportionation reaction in which P gets oxidised as well as reduced.5. With Conc. HNO
3 and conc. H
2SO
4, it produces H
3PO
4.
Refer the topics HNO3 and H
2SO
4 for this.
USES:1. Used to prepare phosphoric acid(H
3PO
4) which is used to make fertilizers.
2. Red phosphorous is used in match industry.
20
METALS
AN OVERVIEW OF METALLURGICAL PROCESSES:A few metals like Au, Ag, Pt etc. are available in the free or uncombined state in the earth crust.But a large number of metals like Na, Mg, Al, Cu, Fe, Sn, Pb, Cr etc. that we know are notavailable in the free state. They are found in the combined state in the form of compounds calledminerals. Say for example the metal aluminium is available in a mineral called bauxite whosecomposition is Al
2O
3.2H
2O. Minerals are mostly available inside the earth(earth crust). Some
minerals(like rock salt) are also available in the soluble form in sea water. Not all minerals areused to recover free metals from them. For example, haematite(Fe
2O
3) and iron pyrite(FeS
2)
are the two minerals containing Fe. But iron is extracted from haematite and never from ironpyrite. Thus the mineral from which we can get the metal most economically and convenientlyis called an ore. Iron pyrite is not an iron ore while haematite is. After the mineral is minedfrom the earth, it is subjected to various processes in order to produce pure metal from it.Besides the main compound of the mineral(say Al
2O
3 in bauxite ore), the ore contains a lot of
unwanted impurites such as silica(sand), rock matter, clay and other metals etc. which have toto be removed. These impurites are called gangue. The ore is subjected to various processes inorder to produce pure metal. The process of extracting pure metal from its ore is calledmetallurgy. The different metallurgical steps are briefly outlined below.1. CRUSHING AND PULVERIZATION:First the large pieces of ores(like large stones) are crushed to small pieces and thenpowdered(pulverization) in different mills.2. DRESSING OR CONCENTRATION:The process of removing gangue(impurites) from the main compound of the mineral is calleddressing or concentration. For example, bauxite contains alumina(Al
2O
3) as the main ore alongwith
several impurites(gangue). Separation of pure Al2O
3 from the rest of the impurites is called
dressing or concentration. The readers are suggested not to mistake the term concentration usedhere in metallurgy with concentration of a solution. The two meanings are different. Thereare different types of concentration processes in metallurgy, some of which are discussed below.(a) Gravity Separation: In some ores, the gangue particles are lighter than ore particles.When powdered ore, taken in a stair-case is flushed with water, gangue particles are washedaway with flowing water and the heavier ore particles stay back.(b) Magnetic Separation: If either gangue or ore particles are ferromagnetic(attractedby a magnet), then ore particles can be separated from gangue particles by the help of a magnet.Magnetic ores of iron(haematite etc.) are separated from the nonmagnetic gangue by this method.(c) Froth Floation Method: This is applicable mostly to sulphide ores likegalena(PbS), zinc blende(ZnS) etc. The ore particles have a special property of adhering withoil. In other words the ore particles stick with oil. When the powdered ore is mixed with someoil(pine oil) and the mixture is agitated in a large quantity of water. The ore particles stick to theoil and remains in the upper layer forming a froth(you know that oil is lighter than water and doesnot mix with it). This oil-water froth containing ore particles is separated to another chamberfrom which the ore particles are recovered from the oil. The impurites remain back in the firstchamber at the bottom.(d) Leaching: In this process, the powdered ore is treated with a solvent, the ore
21
particles are dissolved in that solvent while the gangue particles do not dissolve. On filtration, thedissolved ore solution is obtained in the filtrate and the insoluble gangue remains in the residue.Finally the ore is recovered from the solution by some technique. For example, bauxite orecontaining Fe
2O
3 as impurity is heated with NaOH solution to dissolve Al
2O
3 in the form of
metaaluminate(NaAlO2).
Al2O
3 + NaOH --------> NaAlO
2 + H
2O (Metathesis: Ampoterism)
Then the solution, after separation from the gangue, is heated with fresh water to producegelatinous white precipitate of Al(OH)
3.
NaAlO2 + H
2O -----heat-----> Al(OH)
3(ppt.) + NaOH (M)
Finally white Al(OH)3 precipitate is dried and strongly heated to give pure alumina(Al
2O
3)
Al(OH)3 ------heat-----> Al
2O
3 + H
2O (M)
2. CALCINATION:After the gangue materials are separated, the ore is heated in the absence of air. This is calledcalcination. During calcination,
(i)Moisture(H2O) is mainly removed.
(ii)If the ore is a carbonate ore, it decomposes to produce its oxide and CO2.
3. ROASTING:After calcination the ore is heated strongly in presence of air(O
2) in a furnace called reverberatory
furnace. During roasting the following main events occur.(i)The impurites like S, P, As, Sb etc. if present in the ore are oxidised to their oxides and
volatilised out. Note that not all impurites present in the ore are removed in the process ofconcentration. Some are removed at this stage of roasting.
S + O2 -------> SO
2↑; P
4+O
2 ---------> P
2O
5↑; As + O
2 --------> As
2O
3↑ etc.
(ii)The non-oxide ores are converted to the oxide ore. For example, ZnS(zinc blende) isconverted to ZnO, galena(PbS) is converted to PbO and so on.
ZnS + O2 -------> ZnO + SO
2(R) S from -2 to +4 and O from 0 to -2.
4. EXTRACTION OF FREE METALS FROM METALLIC OXIDES:In roasting process we get oxide of the metal. Now our job would be to get free metal
from the metallic oxide. This can be done in many ways.(i)SMELTING:
This is the reduction of the metallic oxide by C or CO. Metals like Fe, Pb, Zn etc. are extractedby this method. This is done in a furnace called blast furnace. The temperature of the furnaceis so high that metal is obtained in the liquid state at the bottom of the furnace.
ZnO + C --------> Zn + CO (R) Zn from +2 to 0 and C from 0 to +2.Fe
2O
3 +CO -----> Fe + CO
2(R)Fe from +3 to 0 and C from +2 ro +4
Slag Formation:During smelting operation, another event occurs. This is called slag formation. Just before smelting,the roasted ore is mixed with another substance called FLUX. It has been said before that someimpurites always remain even after concentration. This impurity(gangue) will react with the fluxadded during smelting to produce what is called SLAG. Slag has lower melting point and themolten slag is lighter than molten metal and therefore remains above the molten metal. Slag isthus removed separately from the molten metal. A large quantity of impurities present in themetal are removed in the form of slag.The flux is chosen according to the nature of the impurity(gangue). If the gangue is acidic(say
22
SiO2), then the flux selected should be basic(CaO) and vice versa. Then only reaction between
them is possible.Flux + gangue ----------> SLAG
CaO(basic gangue) +SiO2(acidic flux) --------> CaSiO
3 (calcium silicate) Slag
SiO2(acidic gangue) + CaO(basic flux) ---------> CaSiO
3 (calcium silicate) Slag
Note that the basic flux CaO is used in the form of lime stone(CaCO3) which on heating
decomposes to CaO which reacts with the acidic impurites. Sand(SiO2) is used as the acidic
flux.(ii)ELECTROLYTIC REDUCTION:
Very active metals such as Na, K etc.(alkali metals), Mg, Ca etc.(alkaline earth metals) and Alare not extracted by the chemical reduction of their oxides by reducing agents such as carbon orcarbon monoxide. This is because, these metals themselves are very good reducing agents. Inthe language of electrochemistry, we say that the oxidation potentials(refer the chapter,electrochemistry) of these electrodes are high and they have little tendency to be reduced fromtheir +ve oxidation state to zero state. Such metals are obtained by the electrolysis of theirfused(molten) compounds. For example, the electrolysis of fused NaCl gives Na at cathode andCl
2 gas at anode. Electrolysis of molten alumina(Al
2O
3) gives Al at cathode and O
2 gas at anode.
(iii)ALUMINOTHERMIC PROCESS: (Reduction by Al):Al is a strong reducing agent and is used to reduce oxides of Cr, Mn etc. which lie below Al in theelectrochemical series to the corresponding metals.
Al + Cr2O
3 --------> Cr + Al
2O
3(R) (R) Al from 0 to +3 and Cr from +3 to 0.
Al + Mn3O
4 --------> Mn + Al
2O
3(R) Al from 0 to +3 and Mn from +2.66 to
0.
Other uncommon reduction processes are also there but we shall not discuss about them now.
5. REFINING OR PURIFICATION OF METALS:The metal obtained after reduction step is not 100% pure. A very small amount of
impurities still exists at this stage. This impure metal is subjected to further purification to getnearly 100% pure metal. This is called refining of metal. There are several methods of refiningan impure metal.
(i)Electrolytic Refining:This is one of the best methods of refining. In this method, the impure metal is made as the anodeand a strip of pure metal is made as cathode in an electrolytic cell. The electrolyte used should bea salt solution of the metal. For example, in refining of copper, CuSO
4 solution is used as the
electrolyte. In this case, anode is made of impure copper while the cathode is made of a thin stripof pure copper. When electric current is passed through the electrolyte solution, Cu dissolvesfrom the anode to form Cu2+ and Cu2+ thus formed is deposited at cathode as Cu. The anodeslowly becomes thinner and the cathode becomes thicker and all the pure Cu is thus transferredfrom anode to cathode. The impurities present in the impure metal cannot dissolve and settledown there in the anode compartment as insoluble substance called anode mud. In coppermetallurgy, many valuable metals like gold and silver which remain as impurities with copper arefound in this anode mud.
23
At anode: (Impure metal): Cu -------------> Cu2+ + 2eAt cathode:(Pure metal): Cu2+ + 2e-------> Cu(ii)Distillation Method:
Volatile metals like Zn, Hg whose boiling points are less are separated from other nonvolatileimpurites just by distilling the impure metal in a retort. The low boiling metals distil off and arecondensed in the receiver to get pure metal. The residue in the retort contains the nonvolatileimpurities.
(iii)Liquation:Metals having lower melting points are separated from other metals whose melting points aregreater by this method. The impure metal is kept on the top of a inclined plane. The inclinedplane is heated slowly so that the temperature increases gradually. First the metal having lowerboiling point will melt and trickle(flow)down the slope of the inclined plane leaving behind thepure metal on the slope of the plane. Impure lead which contains zinc as impurity is purified bythis method. Zn has a lower melting point and melts first and flows down the inclined planeleaving infusible Pb on the inclined plane.
(iii) Polling:Polling is a method employed in the purification of copper which contains cuprous oxide as animpurity. The impure metal is melted and green wooden poles are used to agitate the moltenimpure copper. The heat of the copper makes the pole emit a gas which reduces the cuprousoxide to copper
CHEMISTRY OF SOME IMPORTANT METALS
SODIUM(Na):Sodium is one of the most reactive elements belonging to alkali metals. It is soft and can be cutby a knife. It reacts vigorously with water and air, so is stored under kerosene. It is silvery whitein colour observed when it is freshly cut but the colour fades if exposed to air due to formation ofits oxide,hydroxide and carbonate. Its melting point is 980C close to boiling point of water.
EXTRACTION:(METALLURGY):Ores: 1.rock salt(NaCl) deposits in many areas and from sea water(brine)
2. Chile salt petre(NaNO3) 3. Glauber salt(Na
2SO
4.10H
2O).
4. soda(Na2CO
3) 5.Salt cake(Na
2SO
4)
Electrolytic Reduction (Down's process):Sodium metal is extracted by the electrolysis of molten NaCl containing CaCl
2 using iron
cathode and graphite anode at about 5800C. CaCl2 is mixed with NaCl for the following reasons.
(i)Melting point of the mixture is 5800C while that of pure NaCl is nearly 8000C. At thishigh temperature sodium metal would volatilise out forming a metal fog(mist) which can catchfire. A part of sodium vapour consenses in the molten NaCl to form colloidal solution whichprevent the flow of ions and hence conduction.
(ii)The electrical energy consumed is less if electrolysis is carried out at 5800C i.e theprocess becomes economical.
As usual, Na is obtained at cathode and Cl2 at anode.(see chapter electrochemistry)
24
PROPERTIES:1. With water: It reacts vigorously with water producing H
2 gas. Often it catches fire in
water.Na + H
2O --------> NaOH + H
2(R) Na from 0 to +1 and H from +1 to 0
2. With air: In moist air it loses its lustre due to formation of oxide, hydroxide and carbonate.Na + O
2 ------> Na
2O, (R) Na from 0 to +1 and O from 0 to -2.
Na2O + H
2O -------> NaOH (M)
NaOH + CO2 -------> Na
2CO
3 + H
2O (M)
Due to the fast reaction of the metal with water and air, it is kept under kerosene.3. Burning in air(O
2): When Na burns in air, it imparts golden yellow flame and produces
mostly sodium peroxide. Some oxide is also formed.
+-1+10
Na2O2Na O2 (R) and-2
++10Na2ONa O2 (R)
4. With Acids: Na liberates H2 from dilute acids(can you guess why?)
Na + HCl ------> NaCl + H2
(R), Na + H2SO
4(dil) -------> Na
2SO
4 + H
2(R)
Find the changes of ON in these reactions by yourself.5. Synthesis reactions: Many nonmetals react with Na to form compounds.
Na + H2 -------> NaH(sodium hydride) (R) Na from 0 to +1 and H from 0 to -1.
Na + Cl2 ------->NaCl (R)
Na + S ------> Na2S (R)
6. As reducing agent: Na is a powerful reducing agent as it reduces oxides of manynonmetals and metals to their free elements.
Na + SiO2 -------> Na
2O + Si (R) Na from 0 to +1 and Si from +4 to 0
Na + Al2O
3 ------> Na
2O + Al (R)Na from 0 to +1, Al from +3 to 0.
7. With NH3: When sodium reacts with liquid ammonia in presence of some impurites like
Pt, MnO2, or when dry NH
3 reacts with Na at higher temperature(200-3000C)hydrogen gas is
evolved alongwith the formation of sodium amide(sodamide).Na + NH
3 -------> NaNH
2 + H
2(R) Na from 0 to +1 and H from +1 to 0.
USES: 1. Sodium vapour lamps to emit golden yellow light2.Liquid Na is used as a coolant in nuclear reactors(refer the topic radioactivity)3.Preparation of tetraethyl lead which is used as an antiknock agent in petrol.
SOME COMPOUNDS OF SODIUM:
1. SODIUM HYDROXIDE(CAUSTIC SODA): NaOHIt is prepared by the electrolysis of NaCl solution(brine or sea water) using mercury ascathode.The cell used is called Castner and Kellner cell. Na(Hg) i.e sodium amalgam isformed at cathode and Cl
2 is formed at anode. The sodium amalgam is allowed to react with
water to give NaOH (Refer the topic electrolysis for details).At cathode: Na + + Hg + e --------> Na(Hg) (sodium amalgam)
Na(Hg) + H2O --------> NaOH + H
2
At anode: 2Cl- ----------> Cl2 + 2e
25
PROPERTIES:It is a deliquescent white crystalline solid. Deliquescent means it absorbs moisture and dissolvesin it. Its solution is bitter to taste, soapy to touch and corrosive to handle.It is highly soluble inwater.Some of the reactions of NaOH is depicted in the SAQ below. Predict the products of your own.The response to SAQs can be referred only for verification purpose.SAQ 8: Predict the products when NaOH reacts with the following. Give the type of reactionand show changes in ON for redox reactions.
(i) HCl (ii)CO2(limited and excess) (iii)HNO
3(dil) (iv)H
3PO
4
(v)SO2
(vi)NO2(vii)Al
2O
3(viii)Sn(OH)
2(ix)PbO
(x)Cl2(cold and dilute/hot and conc.) (xi)P
4(white) (xii)S
(xiii)Al (xiv)Sn and Zn (xv)FeCl3
(xvi)AlCl3(limited and excess) (xvii)SnCl
2(limited and excess) (xviii)NH
4Cl(Heat)
SAQ 9 : How do you test the presence of Na+ ion in a salt of sodium say, NaCl or NaNO3 etc.
CALCIUM(Ca)Calcium is present in our bones and teeth as calcium phosphate. It is hard and a reactive metal,but not as reactive as sodium. It is not stored under kerosene like sodium. It is silvery white incolour but the colour fades when exposed to air due to formation of its oxide, hydroxide andcarbonate. It is malleable and ductile and is a good conductor electricity.Ores: Carbonate(CaCO
3): Limestone, chalk, marble, calcite etc,
Dolomite: CaCO3.MgCO
3, Gypsum: CaSO
4.2H
2O,
Phosphorite[Ca3(PO
4)
2], Fluorspar(CaF
2),
Egg shells and shells of sea animals like snail(CaCO3)
EXTRACTION:Like Na, calcium is also a strong reducing agent and cannot be easily extracted by reduction ofits oxide. First the ore say, limestone is converted to calcium chloride by treatment with HCl.Then a mixture of dry CaCl
2 and CaF
2(6:1) is melted and the molten mixture is subjected to
electrolysis at 7500C using iron cathode and graphite anode. Calcium is obtained at cathode andCl
2 is obtained at anode.Write the electrode reactions by yourself. Refer the topic electrochemistry
if required.PROPERTIES:The chemical properties are quite similar to that of sodium. Some of the important chemicalreactions are given in the SAQ below. Try to answer it and check with the response.
SAQ 10 :Predict the products when calcium reacts with the following . Also indicate the type ofreaction(R or M) and show changes in ON if it is a redox reaction.
(i) H2
(ii)C (iii)CO2
(iv)H2O (v)Cr
2O
3
USES:1. As a dehydrating agent 2. As a reducing agent for extracting Be, Cr
26
COMPOUNDS OF CALCIUM:
1. Calcium Oxide(Quick lime or lime):CaOCalcium oxide(quick lime) is prepared by heating calcium carbonate(lime stone, chalk etc.).
CaCO3 ------heat-------> CaO + CO
2(M)
Properties: Some of the properties of CaO are depicted in the following SAQ. Try to answerthem and check with the response.SAQ 11 : How does CaO react with the following. Indicate the type of reaction and show ONchanges for redox reactions.
(i)C(at 20000C) (ii)SiO2(high temp.) (iii)P
2O
5(at high temp.) (iv) H
2O
2. Calcium Hydroxide[Ca(OH)2] or Slaked lime
It is prepared when lime or calcium react with water.Ca + H
2O ------> Ca(OH)
2 + H
2(R), CaO + H
2O -----> Ca(OH)
2(M)
Properties: It is weakly soluble in water. The solution of slaked lime is called limewater.Some important properties are depicted in the following SAQ. Solve of your own and tally withthe response.SAQ 12 : Predict the products when slaked lime reacts with the following. Indicate the type ofreaction and show the changes in ON for redox reaction.
(i)On heating (ii)CO2(limited and excess) (iii)SO
2(limited and excess)
(iv)(NH4)
2SO
4(heat) (v)Cl
2(cold and dil.slaked lime)
(vi)Cl2(hot and conc. slaked lime) (vii)dry Cl
2(dry slaked lime)
SAQ 13 : How shall you test for a calcium salt(Ca2+)?
ALUMINIUM(Al):Aluminium is a silvery white, light metal used in various ways in the pure form or in the form ofalloys with other metals in various areas starting from the light aluminium foil used for packagingto thick sheets used as aeroplane wings. The application of aluminium is extensive in contrast toNa and Ca which have little commercial utility as metals. Aluminum is a highly malleable andductile metal. The ductility is used for making electrical transmission wire. It is a good conductorof electricity although inferior to copper. Because of its low cost, it is extensively used in electricaltransmission. Although aluminium is present abundantly in clay, slate and many types of silicaterocks, it is mainly extracted from its ore BAUXITE which is dihydrate of alumina (Al
2O
3.2H
2O).
Do you know, India is one of the largest producers of aluminium? NALCO(National AluminumCompany) situated at Angul, Orissa is the company which produces aluminium metal from bauxite.EXTRACTION:1. Bauxite ore is crushed and powdered first. It contains Fe
2O
3 as the major impurity.
2. (i) Concentration by Leaching(Baeyer's Process):This method is applicable when bauxite ore contains ironc oxide as impurity. We already knowabout leaching from our earlier discussion . The powdered ore is heated with conc. NaOHwhich dissolves the alumina(Al
2O
3) forming sodium meta aluminate. The impurity Fe
2O
3 does
not dissolve.Al
2O
3 + NaOH -------> NaAlO
2 + H
2O (M: Ampho.)
27
The solution is filtered and the residue containing the impurities is rejected. The filtrate containingmeta aluminate is mixed with water and a little aluminium hydroxide is added onto it and boiled.Sodium metaaluminate is decomposed to gelatinous white precipitate of Al(OH)
3. The small
amount of Al(OH)3 taken initially acts as seed to bring about the decomposition and precipitation
of further quantity of Al(OH)3 from aluminium meta aluminate. This process is called seeding.
NaAlO2 + H
2O -----boil -------> Al(OH)
3(gelatinous ppt.) + NaOH (M)
The precipitate is dried and again strongly heated to get pure alumina(Al2O
3).
Al(OH)3 -----heat-------> Al
2O
3 + H
2O
(ii) Serpek's Process:This method is used when bauxite contains silica as impurity. A mixture of powdered bauxite andcoke is heated in a current of N
2 gas at 18000C to form aluminium nitride.
Al2O
3 + 3C + N
2 ----------> 2AlN + 3CO
During this process, silica is converted to Si which is volatilised out.SiO
2 + C ------> Si + CO
AlN on heating with water produces Al(OH)3.
AlN + 3H2O ------> Al(OH)
3 + 2NH
3
Then Al(OH)3 is strongly heated like the Baeyer's process to give pure alumina.
3. Electrolytic Reduction of Alumina (Hall's Process)The melting point of alumina(Al
2O
3) is nearly 20000C and the boiling point of aluminium(Al) is
18000C. So if electrolysis of pure molten aluminium is carried out, aluminium produced at cathodeis vapourized out. To prevent this to occur, alumina(Al
2O
3) is dissolved in molten cryolite(Na
3AlF
6)
at a temperature of only 9000C. Al2O
3 undergoes dissociation to produce the positive and negative
ions as follows.Al
2O
3 ----------> Al3+ + AlO
33-
Graphite anode and graphite cathode are used for the electrolysis of alumina dissolved in moltencryolite. Al is obtained at cathode and O
2 is evolved at anode.
At cathode: Al3+ + 3e --------> AlAt anode: 4AlO
33- -----------> 2Al
2O
3 + 3O
2 + 12e
4. Electrolytic Refining of Aluminum(Hoope's Process):Aluminium obtained by the above method is not 100% pure. To make it pure, electrolysis methodis adopted. The cell consists of three layers. The bottom layer is the layer of molten impuremetal, the middle layer is a molten mixture of cryolite(Na
3AlF
6) and BaF
2 and the top layer
which is formed during electrolysis is the top layer of molten pure metal. The density of themiddle layer is so adjusted that it is lighter than molten impure metal but heavier than moltenpure metal. In this case the graphite cathode is suspended into the top layer and the bottom layer(graphite lining)acts as anode. In fact the effective anode is impure Al and effective cathode ispure Al. Aluminium dissolves at anode forming Al3+ and rises up through the middle layer and isdischarged as Al metal in the top layer which is the layer of molten pure aluminium.
At anode: Al --------> Al3+ + 3e (Bottom impure layer)At cathode: Al3+ +3e ------> Al (Top pure layer)
PROPERTIES:Al is an active metal as it lies far above H in the electrochemical series. It exhibits amphoterismi.e liberates H
2 both from dilute acids and strong bases(NaOH, KOH). Some of the properties of
aluminium are depicted in the following SAQ. Answer each reaction with proper logic and tallywith the response.
28
SAQ 14 : Predict the products when Al reacts with the following. Indicate the type of reactionand show the changes in ON for redox reaction.
(i)O2( moist air) (ii)H
2O(boiling) (iii)dil HCl, H
2SO
4(iv)NaOH
(v)N2
(vi)Cl2
(vii)Cr2O
3 and Mn
3O
4
(viii)CO2 and SiO
2(ix)ZnSO
4, CuSO
4
USES:1. Cheap household utensils 2. Electricity transmission wiresAlloys of Aluminium: Alloy is a homogenous solution of one metal with other metal(s) presentin small quantities. The properties of alloy is much better than a pure metal. The important alloysof aluminium are:1. Magnalium: Al(95%) + 5%(Mg): construction of airship parts, balance parts2. Duralumin: Al(95%) + Cu(4%) + Mg and Mn (1%): airplane and automobile parts3. Y-alloy: Al(93%) + Cu(4%) + Ni(2%) + Mg(1%): Aircraft parts
IRON(Fe)Iron is the most common metal in human civilization. Do you know our blood is red due topresence of iron in the haemoglobin? It is also believed that iron is the main constituent of theearth's core(interiror).It plays major role in almost every aspect of everyday life. Whether weare using a screwdriver or a washing machine, or riding in a car or train, the importance andusefulness of iron as a structural material is remarkable. Although plastics have partially replacedthe use of iron, still iron is considered as the hero of all metals as regards the versatility of itsapplication. Iron is not found in its free state and is mostly available as two oxide ores, haematiteand magnetite. In the pure state, iron looks silvery white lustrous metal. Unfortunately the puremetal quickly corrodes. It reacts with moisture(H
2O) and air(O
2) to form rust. Rust is a hydrated
oxide of iron(Fe2O
3.xH
2O). Rust is porous, reddish material that sticks very loosely to the surface
of the iron and usually crumbles or peels off. Thus fresh iron is exposed to the atmospheres tocorrosion and with course of time the whole iron material is disintegrated. Hence iron material isprotected from corrosion(rust formation) by several ways which will be discussed later.
BRIEF METALLURGY OF IRON:Ores: 1.Haematite(Fe
2O
3)
2.Magnetite(Fe3O
4)
3.Siderite(FeCO3)
4.Limonite(Fe2O
3.3H
2O)
In India, haematite ore is generally used to extract iron. Steel Authority of India(SAIL) looksafter the production of iron and steel at different places like Rourkela, Jamshedpur, Bhilai etc.
Concentration:The crushed and powdered ore is concentrated by gravity separation followed by magneticseparation(refer general metallurgy to revise these two processes).Roasting: The concentrated ore is roasted in a reverberatory furnace with excess air. Thefollowing changes occur.
(i)Haematite ore contains impurites like P, S, C, As, Sb etc. which react with O2 and
form their volatile oxides which are removed as gases.
29
P + O2 -----> P
2O
5(R), S+ O
2 ------> SO
2(R)
As + O2 -----> As
2O
3(R) etc. (Find the changes of ON in all these reactions.)
(i)If some iron is present in the form of FeO(ferrous oxide), it is oxidised to ferric oxide.FeO + O
2 -------> Fe
2O
3(R) (Fe from +2 to +3 and O from 0 to -2.)
Smelting:This is done in a blast furnace which is a very tall furnace. Have you seen a tall blast furnaceat any SAIL industry(Rourkela, Bhilai etc)? The roasted ore is mixed with coke(both fuel andreducing agent) and lime stone(flux). The mixture is called charge.(The reader is to note thatthe term charge used in metallurgy is different from electrical charge). Hot air is introduced intothe furnace at the lower part. The charge is fed into the furnace through the upper part. The tallfurnace is divided into four zones with different temperature ranges. The events that occur inthese zones are briefly outlined below. From top to bottom, the zones are
(i)Zone of Reduction (ii)Zone of Slag Formation (iii)Zone of Fusion(iv)Zone of Combustion. Let us discuss the zones. Look to the schematic diagram below
representing the different zones of the blast furnace.
30
(i)Zone of Combustion(1500-16000C): It is the lowermost zone and the temperatureof this zone is the highest. Here carbon(coke taken in the charge) reacts with O
2 gas to form
CO2 and a lot of heat. It is the heat production centre.
C + O2 -------> CO
2 + heat
CO2 formed reacts with excess coke(C) to form CO. Note that CO is the actual reducing
agent to be used in the upper zone.CO
2 + C + heat -------> CO
Some heat is used up in this reaction, so that temperature is slightly reduced at the upper part ofthis zone. So ultimately CO is produced in this zone which rises up to the higher level zones.
(ii)Zone of Reduction(250-7000C): This is the uppermost zone and is farther awayfrom the heat production centre. It has the minimum temperature range. Fe
2O
3 present in the
ore is reduced by CO which is coming from the zone of combustion forming metallic iron(Fe).The reduction occurs in three stages, first +3 state changing to +8/3 state(Fe
3O
4), then +2
state(FeO) and finally 0 state(Fe).Fe
2O
3 + CO ---------> Fe
3O
4 + CO
2(R) Fe from +3 to +8/3 and C from +2 to +4
Fe3O
4 + CO ------> FeO + CO
2(R), Fe from +8/3 to +2 and C from +2 to +4.
FeO + CO --------> Fe + CO2
(R) Fe from +2 to 0 and C from +2 to +4.Iron formed here is solid and sponge like and is called spongy iron. The spongy iron falls downto lowere zones until it reaches the zone of fusion where it melts.
Air(O2) Air(O2)
ore + coke + limestone = charge
slag(CaSiOslag(CaSiO3)
molten iron(Pig iron)
1500-16000C
250-7000C
800-10000C
1200-15000C
zone of combustion
zone of reduction
zone of slag formation
zone of fusion
(Shematic diagram of a blast furace)
31
(iii)Zone of Slag Formation:(800-10000C): This zone is next to zone of reductionfrom the upper side and its temperature is 800-10000C. Two events occur at this zone.(A) The flux CaCO
3 that is present in the charge breaks down at this temperature to CaO
and CO2. CO
2 goes off. But CaO reacts with silica(SiO
2) and P
2O
5 present as impurity(gangue)
in iron and produces slag, calcium silicate and calcium phosphate respectively.CaO(from flux) + SiO
2(impurity) -------> CaSiO
3(slag) (M)
CaO(from flux) +P2O
5(impurity) -------> Ca
3(PO
4)
2(slag) (M)
Slag melts at this temperature and falls down to the bottom of furnace. Molten slag is lighter thanmolten metal and at the bottom of the furnace two layers are formed, upper layer being slag andlower that of metal.(B) The ore still contains some P
2O
5, MnO
2, SiO
2 as impurity. These react with coke present
in the falling charge to give free elements P, Mn, Si etc. which combine with the spongy iron atthis zone.
(iv)Zone of Fusion:(1200-15000C): This is the third zone from the upper side and isnext to zone of combustion from lower side. Its temperature range is 1200-15000C. The spongyiron coming from the upper zone with small amounts of P, Mn, Si and coke melts at this zone at12000C and is collected at the bottom of the furnace. The slag layer lies above the molten metallayer. The molten slag and metal are removed from the furnace through separate holes.Slag(CaSiO
3)is used as a building material in road construction.
This iron which comes from blast furnace is called Pig iron which contain about 95% iron,nearly 2.5-4% carbon and traces of other impurities like Mn, Si, P and S. The pig iron isalso called Cast iron. At a later stage pig iron is remelted and poured in moulds and different ironparts are cast in them. That is why pig iron is also called cast iron.
TYPES OF IRON:1. Cast Iron: It is most impure form of iron containing highest percentage of carbon(2.5-4%) and a very small percentage of P, Si, Mn, S etc. It melts at 10150C. It is hard andbrittle. It is not magnetized easily. It has low ductility. It is used for making rail lines, electricpoles, hot water pipes used in cold countries where the strain applied to iron is minimum.2. Wrought Iron: It is the purest form of iron and contains the lowest percentage ofcarbon (0.1-0.25%) and a trace of other impurities like Si, Mn, P, S etc. It is prepared byremoving the excess carbon from cast iron by oxidising with air. Wrought iron is fairly soft,malleable and ductile and is non-brittle. It can withstand high stress. It can be magnetized easilyand has high resistance towards corrosion.It is used to prepare nails, hooks, bolts etc. which can tolerate sudden impact. It is unsuitable formaking machine parts as it is soft and malleable. Steel is the best form of iron which has all goodvirtues to be used in the multitudinous areas of applications.3. Steel: This is most important commercial variety of iron which contains intermediatepercentage of carbon(0.25 to 2%). Steel is hard and strong. It is neither brittle like pig iron norsoft like wrought iron. Depending on the actual percentage of carbon present, the steel is ofseveral types, such as (i)mild steel(low percentage of carbon ~0.25% ), (ii)hard steel(highpercentage of carbon~ 2%) (iii)steel alloys: small amounts of other metals are mixed withsteel to obtain several alloys of steel. These are given in the following table.
32
Production of Steel:Many methods have been followed to convert pig iron into steel. Among them the popular oneswere (a) Bessemer's process and (b) Open hearth process. In these methods pig iron is convertedto wrought iron by removing almost all carbon and other impurities like P
4, Mn, S, Si from it. This
is done by passing air or O2 gas through the molten pig iron. The impurites burn in O
2 to produce
their oxides which are volatilised out.C + O
2 ------> CO, P
4 + O
2 ------> P
2O
5, S + O
2 ----->SO
2 etc.
Depending on the impurity present in the iron, lining of the Bessemer converter(a special type offurnace) was prepared. For silica impurity dolomite lining and for basis impurity like Mn, silicalining was used in the converter. These are called basic and acidic bessemer's process. Slag isproduced accordingly.
P2O
5 + CaO(from dolomite) ------> Ca
3(PO
4)
2 (slag)
MnO + SiO2 -----> MnSiO
3 (slag)
(All these are redox reactions. Find the changes in ON in all these cases).Carbon burns with blue flame producing CO. When almost all carbon is exhausted, the bluecolour of the flame vanishes, the molten iron is called the wroght iron,which is the purest form ofiron. After making wrought iron, calculated quantity of carbon(0.25-2%) and traces of otherimpurites are mixed with wrought iron to convert it to steel of different grades. These ingredients(C, Mn etc) are not added separately rather are added in the form of an alloy of iron,carbon and manganese called spiegeleisen. This makes the mixing proper andhomogenous.Nowadays, most of the steel industry including our RSP, Rourkela makes use of the BasicOxygen Process previously called the L.D Process.
Basic oxygen process(BOP) :
It is a steelmaking method in which pureoxygen(called the oxygen lance) is blown into abath of molten blast-furnace iron(pig iron) andscrap. The oxygen initiates a series of intensivelyexothermic (heat-releasing) reactions, including theoxidation of such impurities as carbon, silicon,phosphorus, and manganese coverting pig iron intosteel. In Bessemer's method used earlier, air wasused instead of pure oxygen. But BOP methodhas been found to be economical and moreeffiicent.
SAQ 15 : How are the following processes relatedto steel.
(i)Annealing (ii)Quenching (iii)Tempering (iv)Case hardening(v)Nitriding
33
PROPERTIES OF PURE IRON(WROGHT IRON):Pure iron(wrought) is soft and malleable. Its melting point is 15350C. Some of the reactions of Feare depicted in the SAQ below. Answer them and tally.SAQ 16 : Predict the products when Fe reacts with the following giving proper logic.
(i)CuSO4
(ii)AgNO3
(iii)HCl(dil) (iv)H2SO
4(dil)
(v)H2SO
4(conc.) (vi)HNO
3(v. dilute) (vii)conc. HNO
3
(viii)acidified K2Cr
2O
7(ix) moist air (x)air free water (x)Cl
2
Alloys of Steel: Some of the important alloys of steel are as follows.1. Invar: Steel(64%) and Ni(36%): used for making pendulums and measuring tapes.2. Stainless Steel: Steel(86.5%), Cr(11.5%), Ni(2%): used to make all steel artilcles as it
does not get rusted.3. Tungsten Steel: Tungsten or W(14-20% ), Cr(3-8%) and the rest steel: High speed
artilcles are prepared from it.Methods to protect rusting(corrosion) of Fe:A few methods of protecting Fe from rusting are given below.(i) Galvanising: By applying a coating of zinc on the iron surface.(ii) By painting the iron surface with plastics paints(iii) By alloying with other metals like Cr, Ni(stainless steel), W(tungeten steel) etc.
COMPOUNDS OF Fe
1. FeSO4.7H
2O(Green Vitriol)
Ferrous sulphate crystal is called green vitriol. Each FeSO4 contains seven water molecules of
crystallization. It is prepared when Fe reacts with dil H2SO
4. The resulting green solution is
crystallised to get the green crystals of FeSO4.7H
2O. We can also get FeSO
4 from the waste in
the Kipp's apparatus used for producing H2S gas(refer the topic H
2S).
FeS + H2SO
4(dil) ------> FeSO
4 + H
2S (M)
Some of the important properties of green vitriol are depicted below in the following SAQ. Trythem and tally with the response. FeSO
4 is a very good reducing agent as is easily oxidised to the
ferric state.SAQ 17 : Predict the products when FeSO
4 solution react with the following. Study the logic of
each reaction and show the changes in ON.(i)Heating (ii)acidified KMnO
4(iii)acidified K
2Cr
2O
7
(iv)H2O
2(v)Cl
2 water (vi)NO gas
2. FERRIC CHLORIDE(FeCl3):
Ferric chloride solution is reddish brown. It is prepared by the following ways.Fe + Cl
2 ------> FeCl
3(R: synthesis: show the changes in ON)
Fe(OH)3 + HCl ------> FeCl
3 + H
2O (M: neutralisation)
Properties:Anhydrous FeCl
3 is a dark red deliquescent solid. The hydrated crystal(FeCl
3.6H
2O) is yellow in
colour. The reactions of FeCl3 are depicted in the following SAQ. Note that FeCl
3 is a good
oxidising agent. With good reducing agents it is reduced to Fe2+ state.
34
SAQ 18 : Give the products when FeCl3 reacts with the following. Give the logic of each
reaction.(i)Strong heating (ii)SnCl
2(iii)H
2S (iv) KI
(v)SO2
(vi)NH4OH soln. (vii)KCNS
(viii)K4[Fe(CN)
6] solution
COPPER(Cu)Pure copper is red in color. Have you seen an old red coin which is made of copper? Copperwas used alongwith silver and gold to make coins in earlier days and for this reason the threemetals were commonly called the coinage metals.The most common ore of copper ischalcopyrite in which it is combined with sulphur and iron(CuFeS
2). Copper is one of the best
conductors of electricity(next to silver) and it is very much ductile i.e it can be drawn into thinwires. These properties have made it useful as electrical transmission wires to supply electricityfrom power stations to every place. Unfortunately copper wires are being increasingly replacedby much inferior aluminium wires as the former is becoming more expensive. Copper was onceused to make buttons for the uniform jackets worn by policemen and the common slang expressionused in US "copper" refers to this practice. Copper in this case means a policeman. Like iron,copper also is corroded slowly in atmosphere by forming a green layer of copper carbonate orcopper sulphate. This green substance is called 'patina' or verdigris'.
Cu + O2 + CO
2 + H
2O --------> CuCO
3.Cu(OH)
2(patina)
(R: Cu from 0 to +2 and O from 0 to -2)But unlike the rust of iron, "patina" of copper protects the copper metal underneath it fromfurther corrosion. The green patina looks so beautiful that people are fond of such corrosion. Aclassic example of the formation of patina was the Statue of Liberty made of copper plates inFrance which is stationed in the offshore of Newyork(USA). After few years of its installationit became entirely green. The patina was cleaned much later for centenary celebrations. Manypeople consider the patina that covers old church steeples (domes) or ancient monuments quitebeautiful and have resisted any attempts to remove it.
EXTRACTION OF COPPER:Ore: 1. Chalcopyrite(CuFeS
2) 2. Copper glance(Cu
2S),
3. Malachite[CuCO3.Cu(OH)
2] 4. Cuprite(Cu
2O)
Copper is mostly extracted from cholcopyrite ore. The steps involved in its metallurgy of copperfrom chalcopyrite ore are briefly outlined below.1. Concentration by Froth Floatation Process:The crushed and powdered ore is concentrated by froth floatation process as it is a sulphide ore.Refer the chapter on general metallurgy for details.2. Roasting: The concentrated ore is roasted in a reverberatory furnace at 1400-15000C inwhich the following main reactions take place.
CuFeS2 + O
2 -----roasting----> Cu
2S + FeS + SO
2(R)
Cu from +2 to +1 and S from -2 to +4; there is another reduction here- O goes from 0 to -2)The FeS is partially oxidised to FeO, while Cu
2S does not. Cu
2S does not undergo oxidation
easily.
35
FeS + O2 ------> FeO + SO
2(R: O from 0 to -2 and S from -2 to +4)
Besides this, the impurites like P4, S, As etc. are removed as their volatile oxides during roasting
process.S + O
2 -----> SO
2, P
4 + O
2 -----> P
2O
5, As + O
2 ------> As
2O
3
All these are redox reaction. See the changes in ON by yourself.3. Smelting: The roasted ore contains Cu
2S and (FeS + FeO). This is mixed with the flux
silica(sand) and coke(fuel) and charged to a blast furnace. The following events occur duringsmelting.(i) A part of Cu
2S is oxidised to Cu
2O. Here also a large part of Cu
2S remains unchanged.
Cu2S + O
2 -------> Cu
2O + SO
2(R: S from -2 to +4 and O from 0 to -
2)(ii) FeS is converted to FeO:
FeS + O2 -----> FeO + SO
2(R: see the changes in ONs)
(iii) Slag formation: FeO reacts with silica(SiO2) which is present as flux to give FeSiO
3
slag. Maximum iron is removed in this step due to slag formation.FeO(impurity) + SiO
2 (flux) --------> FeSiO
3 (slag) (M: Neutralisation)
The molten slag being lighter forms the upper layer at the bottom of the furnace and is separatelyremoved. The heavier lower layer contains a mixture of Cu
2S(large part), Cu
2O and a little FeS.
This mixture is called MATTE. The molten matte is removed and subjected to another processcalled bessemerization. Note that metallic copper is not obtained during smelting process aswas the case in iron metallurgy.4. Bessemerization: The molten matte obtained from blast furnace is mixed with freshsand(flux) and heated with air in another furnace called bessemer converter. Following eventstake place at this stage.(i) The small amount of FeS present is oxidised to FeO and FeO reacts with SiO
2(flux) to
form slag. Slag forms the upper layer and is removed.FeS + O
2 ------> FeO + SO
2(R),FeO + SiO
2 ------> FeSiO
3 (slag) (M)
(ii) Cu2S is partly oxidised to Cu
2O.
Cu2S + O
2 -------> Cu
2O + SO
2(R)
Now there is nearly 50% each of Cu2S and Cu
2O. The O
2 supply is then cut off.
(iii) Cu2S reacts with Cu
2O to give Cu. This is a self-reduction process. No other reducing
agent is used here. Oxygen(air) is also not used in this step.Cu
2S + Cu
2O -----------> Cu + SO
2(R: Cu from +1 to 0 and S from -2 to
+4).This type of reduction is very much unique in the metallurgy of copper which is not formed bythe reduction of its oxide by any reducing agent like C or CO, rather is formed by the self-reduction reaction as shown above. The molten copper obtained in this step is poured in sandmoulds. When it is cooled, dissolved SO
2 escape from its surface leaving behind blister marks
on it. That is why it is called blister copper which is 98% pure.5. Electrolytic Refining: Impure copper(blister copper) is made as anode and a strip ofpure copper is made cathode. CuSO
4 in dilute H
2SO
4 is used as electrolyte. On electrolysing the
solution. copper dissolved from the impure anode and pure copper gets deposited on cathode.The impurities present in copper like Ag, Au etc. cannot dissolved and settle down at the anodecompartment and forms the anode mud. For more details refer the topic, 'general metallurgy'.
36
PROPERTIES:Some important properties of copper are depicted in the following SAQ. Try them and tally withthe response. Note that copper lies below hydrogen in the electrochemical series and so itcannot displace hydrogen from water or dilute acids. Also note that Cu exhibits two oxidationstates, +1(ous) and +2(ic).SAQ 19 : Predict the products when copper reacts with the following. Give proper logic to eachreaction and show the changes in ON for the redox reactions.
(i)HCl(dil.) (ii)conc. HCl in presence of air (iii)With O2
(iv)conc. H2SO
4(v)conc. HNO
3(vi)Cl
2(vii)NO (viii)AgNO
3 soln.
(ix)ZnSO4 soln. (x)AuCl
3 soln.
USES:(i) As alloys: Brass and Bronze are most important alloys of copper.
*Brass(Cu and Zn): used for domestic utensils, catridge cases etc* Bronze(Cu and Sn): used for making statues, coins, bells, medals etc.*Gun metal(Cu, Sn and Zn): used for making guns and machine parts.*Monel metal(Cu, Ni and Fe): used for automobile engine parts, chemical plants etc.*Rolled gold(Cu and Al): used for artificial jewelery.
(ii). Copper compounds like CuSO4 is used to kill various forms of fungi and bacteria. Paints
used for ships' hulls contain copper compounds to prevent the excessive growth of marineorganisms in the surface of the hulls. This growth is called fouling and develops slowly on anysurface exposed to sea water. Fouling is prevented by the application of copper compounds.
COMPOUNDS OF COPPER1. BLUE VITRIOL(CuSO
4.5H
2O)
When CuSO4 is crystallised we get the deep blue coloured pentahydrate called blue
vitriol[CuSO4.5H
2O]. CuSO
4 can be prepared by the following ways.
1. CuO + H2SO
4 ------> CuSO
4 + H
2O (M)
2. Cu(OH)2 + H
2SO
4 ------> CuSO
4 + H
2O (M)
PROPERTIES:It is a blue crystalline compound and soluble in water. Some important properties of CuSO
4 are
depicted in the following SAQ.SAQ 20 : Predict the products when CuSO
4 reacts with the following substances. Give the
logic of each reaction. Show the changes in ON for redox reactions.(i)Heating (ii)NH
4OH solution (iii)KI solution
(iv)K4[Fe(CN)
6] solution(v)Fe and Zn (vi)H
2S
USES:1. Used as fungicide to kill moulds and fungi on trees, vines etc.2. In electroplating: When CuSO
4 solution is electrolysed using other metal say Fe as
cathode, a thin coating of copper is deposited on the iron surface. This is called electroplating.Copper can be electroplated on any metal surface by this method.
37
PRACTICE QUESTIONS1. A bluish green crystalline salt (A) on treatment with dilute hydrochloric acid producesan effervescence and liberates a colourless and odourless gas (B). When (B) is passed throughlime water, a milky white precipitate is first formed which subsequently dissolves when excessof (B) was passed through it. After dissolving (A) in dilute HCl, the resulting solution wastreated with potassium ferrocyanide solution, a chocolate coloured precipitate is formed. Onstrong heating solid (A), a black mass was obtained at the end. Identify A and B and give allequations.2. A white salt (A) on heating in a test tube sublimes and deposits at the cooler part of thetest tube. When an aqueous solution of (A) is boiled with NaOH solution, a pungent smelling gas(B) was evolved. When a glass rod dipped in conc. HCl bottle was shown to the gas (B), densewhite fumes were produced. When a solution of (A) is treated with AgNO
3 solution, a curdy
white precipitate was obtained. This white precipitate was dissolved in dilute ammonium hydroxidesolution. Identify (A) and (B) and give equations.3. A white salt (A) on treatment with dil. H
2SO
4 produces a rotten egg smelling gas, (B).
When a filter paper dipped in lead acetate solution was shown over the gas (B), it turned black.The resulting solution was treated NaOH solution dropwise till excess. First a gelatinous precipitatewas formed which dissolves in excess of NaOH solution forming a colourless solution. Identify(A) and (B) and give all equations.4. A white salt (X) on strong heating gives a reddish brown gas (Y). When a solution of(X) is treated with dil HCl solution, a white precipitate (Z) is obtained which dissolved whileboiling and reappeared on cooling.When a solution of (X) is treated with potassium chromatesolution, a yellow precipitate was obtained. Identify (X), (Y) and (Z) and give all equations.5. A white salt (X) on treatment with dilute HCl, produces a gas (Y) having burningsulphur smell. When gas (Y) is passed through acidified K
2Cr
2O
7, the orange colour of dichromate
turned green. When gas (Y) was passed through a saturated solution of H2S, a yellowish white
suspension(Z) was formed. When the salt solution of (X) was treated with potassium dihydrogenpyroantimonate solution, a white precipitate was obtained. Moreover, salt (X) imparted goldenyellow colour to a bunsen flame. Identify (X), (Y), (Z) and give all equations.
RESPONSE TO SAQs(Inorganic Chemistry)SAQ 1: Because ammonia reacts with them.
NH3 + H
2SO
4 -------> (NH
4)
2SO
4 (M)
NH3
+ P2O
5 + H
2O ------> (NH
4)
3PO
4
SAQ 2:(a) Each decompose to NH
3 and the corresponding acid.
NH4NO
3 -------> NH
3 + HNO
3; NH
4Cl ------> NH
3 + HCl
(NH4)
2SO
4 -------> NH
3 + H
2SO
4.These are metathesis reactions.
(b) At high temperature, NH4NO
2 gives N
2 gas and NH
4NO
3 gives N
2O gas. Refer
section-I for the equations. These are redox reactions.SAQ 3: The ON of Fe in FeS
2 is +2 (not +4 as sometimes wrongly believed). This is ferrous
38
disulphide. S changes from -1 to +4 and Fe changes from +2 to +3 while O changes from0 to -2. Here there are two oxidations and one reductions.SAQ 4: Constant boiling mixture or azeotropic mixture means the composition of the componentsin the liquid state is same as that in the vapour state. For example, 20.4% HCl solution formsa constant boiling mixture. This means, when the solution boils at 1100C, vapour also contains20.4% HCl and the remaining water vapour. Once this composition is reached, it is notpossible to further increase the concentration of HCl by distillation method. We shall learnmore about this in higher classes.SAQ 5 : (i) PbO
2 + HBr -------> PbBr
2 + Br
2 + H
2O (R): Pb from +4 to
+2 and Br from -1 to 0. Red vapours of Br2 are evolved.
(ii) H2SO
4(conc.) + HI ------> SO
2 + I
2 + H
2O (R): S from +6 to +4 and I
from -1 to 0. Violet vapours of I2 are formed.
(iii) P4 + Br
2 ------->PBr
3(R): P from 0 to +3 and Br from 0 to -1.
(iv) PBr3 + H
2O-------> H
3PO
3 + HBr (M) Hydrolysis of PBr
3.
(v) NaBr + H2SO
4(conc.)---> Na
2SO
4 + HBr; (M)
A part of HBr is oxidised by conc. H2SO
4 to form Br
2 as HBr is a very good
reducing agant. So red vapour of Br2 is formed.
H2SO
4 + HBr -------> SO
2 + Br
2 + H
2O (R) Show the
changes.(vi) CuSO
4 + HI ------>CuI
2 + H
2SO
4(M).
Then CuI2 will disproportionate as follows.
CuI2---------> Cu
2I
2 + I
2(R): Cu from +2 to +1 and I from -
1 to 0.So ultimately Cu
2I
2, I
2 and H
2SO
4 are formed. Add the two equations after
proper balancing and write the net balanced equation of your own.SAQ 6 : (i)H
2O
2 + NaOCl ------> O
2 + NaCl + H
2O(O from -1 to 0; Cl from +1 to
-1)(ii)H
2O
2 + Br
2 --------> O
2 + HBr + H
2O (show the changes)
SAQ 7 :(i)Cu + HNO3(conc.) ------> Cu(NO
3)
2 + NO
2 + H
2O
(ii) Mg + HNO3(mod. conc.) -------> Mg(NO
3)
2 + NO + H
2O
(iii)Fe + HNO3(v.dil.) ------> Fe(NO
3)
2 + NH
4NO
3 + H
2O
(iv)Zn + HNO3(dilute) --------> Zn(NO
3)
2 + N
2O + H
2O
SAQ 8 :(i)NaCl + H
2O(M) (ii)Na
2CO
3(limited) and NaHCO
3(excess) (M)
(iii)NaNO3 + H
2O (M) (iv)Na
3PO
4 + H
2O(M) (v)Na
2SO
3 + H
2O (M)
(vi)NaNO2 + NaNO
3 + H
2O (Redox: Dispropr.: N from +4 to +5 and from +4 to
+3)(vii)NaAlO
2 + H
2O(M: Ampho.) (viii)Na
2SnO
2 + H
2O(M: Ampho.),
(ix)Na2PbO
2 + H
2O(M: Ampho.)
(x)cold and dilute:NaCl + NaOCl + H2O(R: dispropr.: Cl from 0 to +1 and from 0 to -1),
Hot and conc: NaCl + NaClO3 + H
2O(R: dispropr: Cl from 0 to -1 and 0 to +5)
(xi)PH3 + NaH
2PO
2(R: dispropr.: P from 0 to -3 and 0 to +1)
(xii)Na2S + Na
2S
2O
3 + H
2O (R:dispropr: S from 0 to -2 and 0 to +2)
(xiii)NaAlO2 + H
2(R: Ampho.: Al from 0 to +3 and H from +1 to
39
0),(xiv)Na
2SnO
3 + H
2(R: Ampho.: Sn from 0 to +4, H from +1
to 0);Na
2ZnO
2 + H
2(R: Amph.)
(xv)Fe(OH)3(reddish brown ppt.) + NaCl (M),
(xvi)Al(OH)3(gelatinous white ppt.) + NaCl (M)
Excess: NaAlO2(soluble) + H
2O (M: Ampho.)
(xvii)Sn(OH)2(white ppt) + NaCl (M)
Excess: Na2SnO
2(soluble) + H
2O (M: Ampho.)
(xviii)NH3 + NaCl + H
2O (M)
SAQ 9 : (i)When a sodium salt solution is treated with potassium dihydrogen pyroanitmonatesolution, a white precipitate is obtained. This is a double replacement(metathesis) reaction.NaCl + K
2H
2Sb
2O
7 ---------> Na
2H
2Sb
2O
7(white ppt.) + KCl
(ii) When the salt is put in a flame, it imparts golden yellow colour to the flame.SAQ 10 :(i)CaH
2(R) Ca from 0 to +2 and H from 0 to -1.
(ii)CaC2
(R): Ca from 0 to +2 and C from 0 to -1(iii)CaC
2 + CaO (R): Ca from 0 to +2 and C from +4 to -1.
(iv)Ca(OH)2 + H
2(R): Displacement:
(v)CaO + Cr (R: Metal displacement)SAQ 11 :(i)CaC
2 + CO (R): C from 0 to -1 and same C from 0 to +2
(ii)CaSiO3
(M)(iii)Ca
3(PO
4)
2(M): note that (ii) and (iii) are acid-base reactions.
(iv)Ca(OH)2
(M) This reaction is highly exothermic i.e a lot of heat is evolved.SAQ 12 :(i)CaO + H
2O(M)
(ii)Limited: CaCO3(milky ppt.) + H
2O (M); Excess: Ca(HCO
3)
2(soluble) (M)
(iii)Limited: CaSO3(milky ppt.) + H
2O (M); Excess: Ca(HSO
3)
2(soluble)
(M) (iv)NH3 + CaSO
4 + H
2O (M)
(v)CaCl2 + Ca(OCl)
2 + H
2O (R: dispropr.) Cl from 0 to -1 and from 0 to +1
(vi)CaCl2 + Ca(ClO
3)
2 + H
2O (R: dispropr.)Cl from 0 to -1 and from 0 to +5. The last
two bits are similar to the reaction to that of NaOH with Cl2(refer the topic Cl
2 or
NaOH)(vii)Ca(OCl)Cl(Bleaching powder) + H
2O(R) (Refer the chapter Chlorine).
SAQ 13 :(i) When you treat the salt solution with ammonium oxalate solution, a white precipitate
of calcium oxalate is formed.CaCl
2 + (NH
4)
2C
2O
4 --------> CaC
2O
4(white ppt.) + NH
4Cl
(ii) Calcium salt imparts brick red colour to the flame.SAQ 14 : (i)Al + O
2 --------> Al
2O
3(R): Al from 0 to +3 and O from 0 to -
2.Al reacts with moist air(dry air has no action on Al) to form an oxide layer which preventsfurther attack by air. That is why aluminium metal does not undergo corrosion like iron.
(ii)Al(impure) + H2O(boiling) ------> Al(OH)
3(gelatinous white ppt.) + H
2 (R)
Al from 0 to +3 and H from +1 to 0.(iii)AlCl
3 + H
2 and Al
2(SO
4)
3 + H
2(R: Metal displacement as Al lies above H)
40
Show the changes in ON by yourself.(iv)NaAlO
2 + H
2(R: Ampho.: Al from 0 to +3 and H from +1 to 0)
(v)AlN (R: synthesis: Al from 0 to +3 and N from 0 to -3)(vi)AlCl
3(R: synthesis: give the ON yourself)
(vii)Cr + Al2O
3; Mn + Al
2O
3(R: Metal displacement as Al lies above Cr
and Mn.Show the changes in ON by yourself).(vii)C + Al
2O
3; Si + Al
2O
3(R: Displacement: Al is a strong reducing agent)
C and Si change from +4 to 0 while Al from 0 to +3(viii)Zn + Al
2(SO
4)
3; Cu + Al
2(SO
4)
3(R: metal displacement: Al lies above Zn
and Cu: show the changes in ON by yourself)SAQ 15 :(i)Annealing: Steel is first heated to red hot state and then slowly cooled. This produces softsteel which is ductile. This is called annealing(ii)Quenching: When red hot steel is suddenly cooled by pouring water onto it, it produces veryhard and brittle steel. This process is called quenching of steel.(iii)Tempering: It is the heating the quenched steel not to a very high temperatuure(below redhot) and then slowly cooling(annealing) to get steels exhibiting different colours. Yellow steel isobtained when heated to 200-2300C, blue steel is obtained by heating to 3000C and so on.This isbecause of the formation of different types of oxides of iron on the surface of iron.(iv)Case Hardening: This is the process of making the surface of soft or mild steel hard whileinterior remains soft. This is achieved by heating mild steel with charcoal to some high temperatureand plunging it onto oil. Quenching occurs only at the surface producing a thin coating of hardsteel.(v)Nitriding: The process of forming a hard coating of iron nitride(FeN) on steel is called nitriding.Steel is heated in the presence of dry ammonia at 500-6000C for 3-4 days to form coating ofiron nitride.SAQ 16 : (i)FeSO
4 + Cu (R: Displacement: Fe from 0 to +2 and Cu from +2 to 0)
(ii) FeSO4 + Ag ( R: Displacement) (iii)FeCl
2 + H
2(R: Displacement)
(iv)FeSO4 + H
2(R: Displacement)
(v)FeSO4 + SO
2 + H
2O (R: Fe from 0 to +2 and S from +6 to +4).
(vi)Fe(NO3)
2 + NH
4NO
3 + H
2O (R: Fe from 0 to +2 and N from +5 to -3)
Do you remember that with very dilute HNO3, ammonia gas is formed which react with
nitric acid to give ammonium nitrate.Note that some Fe(NO3)
3 is also formed.
(vii)Metal becomes passive when treated with conc. HNO3. This is called passivity of
metals. This property is shown by Al, Fe, Co, Ni and Cr(already discussed in the topic HNO3).
Once the metal is passive, it does not react with any other chemical. The passivity is believed tobe due to the formation of an oxide coating on the surface of the metal which does not allow theentry of further acid inside the metal. Thus its reactivity stops. But to this author, the actualcause of passivity is not yet known. If the explanation given above(oxide layer theory) iscorrect then why other metals do not become passive with conc. HNO
3, why only few
metals?(viii)Same as bit (vii). The metal become passive with strong oxidising agents like
dichromate, permanganate.
41
(ix)Iron gets rusted when kept in moist air. This is called corrosion. The rust eats awayslowly all iron. Rust is a hydrated Fe
2O
3.
Fe + O2 + H
2O --------> Fe
2O
3. x H
2O (x is variable) R:
(Fe from 0 to +3 and O from 0 to -2)(x) No reaction. Since there is no oxygen in water, rust will not be formed.(xi)FeCl
3(R: see the changes by yourself)
SAQ 17 : (i) FeSO4.7H
2O -----3000C----> FeSO
4(anhydrous) + 7 H
2O
When the water of crystallization molecules go out on heating at 3000C, we get anhydrousFeSO
4. On strong heating FeSO
4 decomposes to Fe
2O
3 alongwith the liberation SO
2 and SO
3
gases.
FeSO4 Fe2O3 SO2 SO3+ ++2 +3+6 +4strong heating
(R)
(ii) K2SO
4 + MnSO
4 + Fe
2(SO
4)
3 + H
2O (R: Mn from +7 to +2 and Fe from +2 to +3).
The pink colour of KMnO4 is discharged. This reaction you have studied many times.
(iii)K2SO
4 + Cr
2(SO
4)
3 + Fe
2(SO
4)
3 + H
2O (R: Cr from +6 to +3 and Fe from +2
to +3). The orange colour of K2Cr
2O
7 turns green due to Cr
2(SO
4)
3. This is another familiar
reaction. Try to balance these equations occasionally by partial equation method for a goodpractice.
(iv)H2O
2 + FeSO
4 + H
2SO
4 ------> Fe
2(SO
4)
3 + H
2O
(R: O from -1 to -2 and Fe from +2 to +3). This reaction we have also studied in thetopic H
2O
2. We know that in all redox reactions of FeSO
4, sulphuric acid has to be used as the
helper, otherwise FeSO4 cannot be oxidised to Fe
2(SO
4)
3.
(v)Cl2 + FeSO
4 + H
2SO
4 -------> HCl + Fe
2(SO
4)
3
(R: Cl from 0 to -1 and Fe from +2 to +3)(vi)When nitric oxide gas is passed through FeSO
4 solution, the solution turns dark brown
due to formation of the compound Fe(NO)SO4 or FeSO
4.NO called nitroso ferrous sulphate.
When you go to higher stage you shall know that the its actual formula is [Fe(NO)(H2O)
5]SO
4.
SAQ 18 : (i) FeCl2 + Cl
2 (R: dispropr.)
(ii)SnCl4 + FeCl
2(R: Fe from +3 to +2 and Sn from +2 to +4).
(iii)S+ FeCl2 + HCl (R: Fe from +3 to +2 and S from -2 to 0).
(iv)FeCl2 + I
2 + KCl (R: Fe from +3 to +2 and I from -1 to 0)
(v)FeCl2 + H
2SO
4 + HCl (R: Fe from +3 to +2 and S from +4 to +6).
Note that SO2 is oxidised to SO
3 which react with H
2O forming H
2SO
4.
(vi)Fe(OH)3(reddish brown ppt.) + NH
4Cl (M:double displacement,
precipitation)(vii)Fe(CNS)
3(blood red colored ppt.) + KCl (M: double displ./preci.)
(viii)Fe4[Fe(CN)
6]
3(ferric ferrocyanide) + KCl (M: double displ./ preci.)
This ferric ferrocyanide is a blue colour precipitate and is called prussian blue. The actualformula of prussian blue is KFe[Fe(CN)
6] i.e potassium ferric ferrocyanide which is sometimes
written as Fe4[Fe(CN)
6]
3. The Fe outside the bracket is in the +3(ic)state and inside the bracket
is in the +2(ous) state. In this reaction the ONs do not change.SAQ 19 :(i) No reaction, as Cu lies below H.
(ii) Cu + HCl(conc.) + O2 -------> CuCl
2 + H
2O (R: Cu from 0 to +2 and O from 0 to -
42
2). Note that H2 gas is not evolved in this case.
(iii) Cu + O2 -----below 11000C ------> CuO(Black)
(R: Cu from 0 to +2 and O from 0 to -2)Cu + O
2 -----above 11000C-------> Cu
2O(Red)
(R: Cu from 0 to +1 and O as ususal)(iv)Cu + H
2SO
4(conc.) -----> CuSO
4 + SO
2 +H
2O
(R: Cu from 0 to +2 and S from +6 to +4).You know that conc. H
2SO
4 is a strong oxidising agent and itself reduced to SO
2.
(v) Cu + HNO3(conc.) -------> Cu(NO
3)
2 + NO
2 + H
2O
(R: Cu from 0 to +2 and N from +5 to +4)You know that conc. HNO
3 is reduced to the reddish brown NO
2 gas.
(vi)CuCl2
(R: find the changes in ON)(vii) Cu + NO -----> CuO + N
2(R: Cu from 0 to +2 and N from +2 to 0)
(viii)Ag + Cu(NO3)
2(R: metal displ. as Cu lies above Ag)
(ix)No reaction, as Cu lies below Zn.(x)Au + CuCl
2(R: metal displ, as Cu lies above Au)
SAQ 20 :(i) When the deep blue coloured blue vitriol crystals are exposed to dry air, two H
2O
molecules spontaneously escape out and convert it to trihydrate. This is called efflorescence.CuSO
4.5H
2O(deep blue)---dry air --> CuSO
4.3H
2O(pale blue) + 2H
2O (M)
On heating to 1000C, two more H2O molecules escape giving the monohydrate(bluish
white).CuSO
4.3H
2O(pale blue)----1000C ----> CuSO
4.H
2O(bluish white) + 2H
2O
On heating the monohydrate to 2300C, we get anhydrous CuSO4.
CuSO4.H
2O -------2300C -------> CuSO
4(white) + H
2O (M)
On strong heating at 7200C, CuSO4 decomposes to CuO, SO
2 and O
2.
CuSO4 --strong heat--> CuO + SO
2 + O
2 (R: S from +6 to +4 and O from -2 to 0)
(ii) CuSO4 + NH
4OH -------> Cu(OH)
2(bluish white ppt.) + (NH
4)
2SO
4 (M: d. repl.)
Cu(OH)2 + 2NH
4OH + (NH
4)
2SO
4 -------> [Cu(NH
3)
4]SO
4(M)
(tetrammine curpric sulphate or cuprammine sulphate).Cuprammine sulphate is an intense blue colour solution. Note that this type of ion which is givenwithin a square bracket are called complex ions, and such substances are called complexsubstances which shall be taken up in higher classes. Thus when you add NH
4OH solution
(or pass NH3 gas) with CuSO
4 solution, first a bluish white precipitate of cupric hydroxide is
formed which with excess of NH4OH(or NH
3 gas) dissolves forming the intense blue solution.
You are supposed to know this much at this stage.(iii) When KI solution is added to CuSO
4 solution and kept for some time, we get a brown
coloured solution due to the formation of free I2. The reaction takes place in two steps.
CuSO4 KI CuI2 K2SO4+ + (M: Double displ
CuI2 Cu2I2 I2+ (R)2
2 X 2
CuSO4 KI Cu2I2 I2 K2SO4+ + +4 2+2 +1-1 0
(R)
In this reaction cuprous iodide(Cu2I
2) and iodine(I
2) are formed.
43
(iv) CuSO4 + K
4[Fe(CN)
6] --------> Cu
2[Fe(CN)
6] (chocolate ppt.) + K
2SO
4 (M)
This is a double replacement(metathesis) reaction Cu2+ exchanges with K+. Thus we get cupricferrocyanide which is a chocolate coloured(dark reddish brown) precipitate.(iv) CuSO
4 + Fe ------> FeSO
4 + Cu, CuSO
4 + Zn------> Cu + ZnSO
4
These are redox(metal displacement) reactions as Fe and Zn lie above Cu.(v) CuSO
4 + H
2S ------> CuS(black ppt) + H
2SO
4(M: double displ./preci.)
ANSWER TO PRACTICE QUESTIONS
1. A = CuCO3; B= CO
2
CuCO3 + HCl ---------> CuCl
2 + CO
2 + H2O (M)
CO2 + Ca(OH)
2(lime water) --------> CaCO
3 (milky white ppt) + H
2O (M)
CaCO3 + CO
2 + H
2O ------> Ca(HCO
3)
2 (soluble)
(M)CuCl
2 + K
4[Fe(CN)
6 ---------> Cu
2[Fe(CN)
6] (chocolate ppt.) + KCl (M)
CuCO3 ------heat--------> CuO(black) + CO
2
2. A = NH4Cl ( a volatile substance which sublimes on heating); B= NH
3
NH4Cl + NaOH -------heat----> NH
3 + NaCl + H
2O (M)
NH3 + HCl -----> NH
4Cl (dense white fumes) (M)
NH4Cl + AgNO
3 -------> AgCl(curdy white ppt.) + NH
4NO
3(M)
AgCl + 2 NH4OH -------> [Ag(NH
3)
2]Cl(soluble)+ 2H
2O (M)
The soluble compound is called diammine silver chloride which is a complex compound.You shall know about it in higher classes.
3. A = Al2S
3; B = H
2S(rotten egg smelling)
Al2S
3 + H
2SO
4 -------> Al
2(SO
4)
3 + H
2S (M)
Pb(CH3COO)
2 + H
2S -------> PbS(black) + H(CH
3COO) or CH
3COOH (M)
Al2(SO
4)
3 + NaOH -----> Al(OH)
3(gelatinous white ppt.) + Na
2SO
4(M)
Al(OH)3 + NaOH -------> NaAlO
2(colourless solution) + H
2O (M: Amph.)
4. X = Pb(NO3)
2; Y= NO
2 (reddish brown gas), Z= PbCl
2
Pb(NO3)
2 -------heat------> PbO + NO
2 + O
2(R: dispropr.)
Pb(NO3)
2 + HCl -------> PbCl
2 + HNO
3(M)
PbCl2 dissolves on boilinng and reappears on cooling.
Pb(NO3)
2 + K
2CrO
4 ------> PbCrO
4(yellow ppt.) + KNO
3
5. X = Na2SO
3; Y= SO
2; Z= S
Na2SO
3 + HCl -------> NaCl + SO
2 + H2O
SO2 + K
2Cr
2O
7 + H
2SO
4 ---------> K
2SO
4 + Cr
2(SO
4)
3 + H
2SO
4 + H
2O (R)
Revise the topic SO2 for details and section-I for balancing.
SO2 + H
2S ------> S(yellowish white) + H
2O (R) Refer the topics H
2S and SO
2
Na2SO
3 + K
2H
2Sb
2O
7 -------> Na
2H
2Sb
2O
7(white ppt.)+ K
2SO
3(M)
