Metals(educationpoint.co.ccc)

8/14/2019 Metals(educationpoint.co.ccc)

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LECTURE NOTES CHEMISTRY STEPS A TCY Program _______________________________________________________________________________________

STEPS____________________________________________________________G e t f r e e c h a p t e r w i s e t e s t s f o r C l a s s X

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The metal oxides are basic in nature. Some metal oxides such as aluminium oxide, zinc

oxide etc show both acidic as well as basic behaviour.

Such metal oxides are amphoteric oxides

Most metal oxides are insoluble in water.

But some of the metal oxide dissolve in water to form alkali.

e.g.alkali

)aq(NaOH2OHONa 22 +

Reactivity with oxygen:

(1) Sodium & Potassium vigorously react with oxygen.

(2) Magnesium, aluminium, zinc, lead etc is covered with thin layer of oxide. This layer

prevents the metal from further oxidation.

Reaction with water:

Reaction of some common metals with water

Metal Reaction conditions ReactionSodium (Na) Reacts vigorously with cold

water to give hydrogen gas.

Na(s) + 2H2O 2NaOH(aq) + H2(g)

cold

Magnesium (Mg) Does not react with cold

water. With boiling water it

gives hydrogen gas.

Mg(s) + H2O MgO(s) + H2(g)

Boiling

Aluminium (Al) Aluminium decomposes

boiling water slowly to give

hydrogen gas.

2Al(s) + 6H2O 2Al(OH)3 + 3H2(g)

boiling

Zinc (Zn) Zinc decomposes boiling

water slowly and steam

rapidly.

Zn(s) + H2O ZnO(s) + H2(g)

Steam

Iron (Fe) Red hot iron reacts with

steam to liberate hydrogen.

3Fe(s) + 4H2O Fe3O4(s) + 4H2(g)

red hot steam iron (II, III) oxide

(ferroso ferric oxide)

Copper (Cu) No reaction even with steam

and at red heat.

Cu + H2O No reaction

Copper


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Reaction with Acid (dilute)

Metal Acid Nature of reaction Reaction

Sodium (Na) Dil. HCl

Dil. H2SO4

Sodium reacts

vigorously with dil.

HCl and dil. H2SO4.

2Na + 2HCl (dil.) 2NaCl + H2(g)

Sodium

Chloride

2Na + H2SO4 (dil.) Na2SO4 + H2(g)

Sodium

Sulphate

Magnesium (Mg) Dil. HCl

Dil. H2SO4

Magnesium reacts

rapidly with dilute

HCl and H2SO4.

Mg + 2HCl (dil.) MgCl2 + H2(g)

Magnesium

Chloride

Mg + H2SO4(dil.) MgSO4 + H2(g)

Magnesium

Sulphate

Zinc (Zn) Dil. HCl

Dil. H2SO4

Zinc reacts with dil.

HCl as well as dil.

H2SO4 at moderate

rate.

Zn + 2HCl (dil.) ZnCl2 + H2(g)

Zinc

Chloride

Zn + H2SO4 (dil.) ZnSO4 + H2(g)

Zinc chloride

Iron (Fe) Dil. HCl

Dil. H2SO4

Iron reacts with dil.

HCl as well as dil.

H2SO4 slowly at

room temperature.

Fe + 2HCl (dil.) FeCl2 + H2(g)

Ferrous

Chloride

Fe + H2SO4 (dil.) FeSO4 + H2(g)

Ferrous

Sulphate

Copper (Cu) Dil. HCl

Dil. H2SO4

Copper does not

react with dil. HCl

and dil. H2SO4 but

slowly dissolves in

dil. H2SO4 in the

presence of air.

No reaction

No reaction

2Cu + 2H2SO4 (dil.) + O2

from air

2CuSO4(aq) + 2H2O

Why metals displace hydrogen from acids?

All metals have a tendency to lose electrons. This tendency of losing electrons depend

upon the nature of the metal. More electropositive metals lose electrons more easily. A

dilute acid contains H+ ions. So when a metal which is more electropositive than hydrogen

is placed in an acid solution it loses electrons. These electrons are then gained by H+ to

produce hydrogen gas.


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In these metal displacement reactions, the more reactive metal acts as a reducing agent

and cation of the less reactive metal as an oxidising agent.

MINERAL: The inorganic elements or compounds which occur naturally in the earths

crust are known as minerals.

ORE: A mineral from which a metal can be extracted on a commercial scale economically

& easily is called an ore.

e.g. Bauxite (Al2O3. 2H2O)

SOME COMMON ORES OF METALS:

Oxide ores Carbonate ores Sulphide ores Halide ores

Bauxite (Al2O3.

2H2O) is an oxide ore

of aluminium.

Limestone (CaCO3) is

a sulphide ore of

lead.

Galena (PbS) is a

sulphide ore of lead.

Rock salt (NaCl) is a

chloride ore of

sodium.Haematite (Fe2O3) is

an oxide ore of iron.

Calamine (ZnCO3) is

a carbonate ore of

zinc.

Copper glance (Cu2S)

and copper pyrites

(CuFeS2) are

sulphide ores of

copper.

Cryolite (Na3AlF6) is

a fluoride ore of

aluminium.

Cuprite (Cu2O is an

oxide ore of copper.

Cinnabar (HgS) is a

sulphide ore of

mercury.

GANGUE: Unwanted earthly material present in an ore is called gangue. Gangue may be

acidic or basic in nature.

METALLURGY:

The extraction of metals from these ores & then refining them for use is known as

metallurgy.

The process of metallurgical operation consists of mainly three steps:

A. Enrichment of ores.

B. Reduction

C. Refining

(A) ENRICHMENT OF ORES:

(a) Hydraulic washing:

It is based on the difference in the densities of the gangue & the ore particles.

The gangue particles are generally lighter as compared to ore particles & get

washed away leaving behind the heavier ore particles.


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(b) Froth Floatation process:

Specifically used to separate the gangue from sulphide ore.

(c) Electromagnetic separation:

This method is based on the difference in the magnetic properties of ore & gangue.

The powdered ore is placed over a convey or belt which moves on two rollers, out of

which one is magnetic.

When the ore passes over the magnetic roller, the magnetic & non magnetic

materials fall separately.

(d) Chemical Separation/ Leaching Process

The process of chemical separation makes use of differences between the chemical

properties of the gangue & the ore.

For example: Aluminium is enriched by dissolving bauxite in sodium Hydroxide & itreacts with the same forming Sodium Aluminate & impurities are left behind

insoluble.

(B) REDUCTION:

The process of obtaining metals from their compounds is known as reduction.

It is easier to reduce metal oxides, as compared to metal sulphides & carbonates.

Froth floatation process. The ore is mixed with a mixture of water and pine oil. When airis blown through the mixture, the oil froth carries the metal sulphides to the top of thetank. The gangue particles sink to the bottom.

Magnetic separation. The finely powdered ore is dropped over a moving belt whichpasses over a magnetic roller. The particles attracted by the magnet form aseparate pile.


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This is employed by Calcination & Roasting.

Calcination: Process of heating an ore strongly in the absence of ore or in the presence of

very limited quantity of air is called calcination.

Calcination of an ore is done to:

Convert a carbonate ore into oxide

Remove moisture / water from the wet/ hydrated ore.

Remove volatile impurities from the ore.

OxideOre

ZinceminCala

)g(COZnOZnCO 23 +

Roasting of ore:

The process of heating an ore (generally a sulphide ore) strongly below its melting point in

the presence of an excess of air is called roasting.Roasting of an ore is done to:

convert a sulphide ore to oxide ore.

Remove volatile impurities & moisture.

oxide

ZincblendeZinc

)g(SO2Zno2O3ZnS 2Heat

2 + +

Differences between calcinations and roasting

Calcination Roasting

During calcinations, the ore is heated in the

absence of air or in the presence of very

limited quantity of air.

Calcination is generally used to convert

carbonate ores into oxide ores.

During roasting, the ore is heated in the

presence of an excess of air.

Roasting is generally used to convert

sulphide ores into oxide ores.

Metals low in the activity series are very unreactive. The oxides of these metals can

be reduced to metals by heating alone. For example: Cinnabar (HgS) is an ore of

mercury when it is heated in air it is first converted into mercuric oxide (HgO).

Mercuric oxide is then reduced to mercury on further heating.

2HgS (S) + 3O2(g) 2HgO + 2SO2

2HgO(S) 2Hg + O2

The metals in middle of the reactivity series such as Iron, Zinc, Lead, Copper are

moderately reactive. The oxides of these metals are reduced by heating with carbon.

Metals high up in the reactivity series are very reactive. They cannot be

obtained from compounds by heating with carbon because these metals have


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more affinity for oxygen than carbon. So these metals are obtained by

electrolytic reduction.

Differences between electrolytic reduction and carbon reduction

Electrolytic reduction Reduction with carbon

This method is used for the reduction of

highly reactive metals.

The metals obtained by this method are

pure and need no further refining.

This method is used for reducing the oxides

of moderately reactive metals.

The metal obtained by this method contain

some impurities and need to be refined

further.

Refining of metals:

The process of purification of impure metals is known as refining of metals.

The method used for refining an impure metal depend upon:

(1) The nature of the element.(2) The nature of impurities present in it.

(a) Liquation method:

(b) Distillation: Volatile metals like mercury & zinc are purified by distillation. The

impure metal is heated in a retort. The pure metal distils over & is condensed in a

receiver & the impurities are left behind in the retort.

(c) Electrolytic Refining:

This is the most widely used method for refining impure metals. Many metals, such

as copper, zinc, tin, nickel, silver gold etc. Impure metal is made as anode & a thin

strip of pure metal is made as cathode.

A solution of the metal salt is used as an electrolyte.

On passing the current through the electrolyte, the pure metal from the anode

dissolves into the electrolyte.

On equivalent amount of pure metal is deposited on the cathode from the electrolyte.

The liquidation method


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Aluminium:

Most abundant metal in the earths crust.

It was first extracted in 1827 from aluminium chloride by using sodium.

AlCl3 + 3Na Al + 3NaCl

Second most widely used metal after iron.

Main ore of aluminium is called bauxite (Al2O3. 2H2O). It contains aluminium oxide,

mixed with impurities like sand and iron oxide. The impurities are removed by

Baeyers process. The pure aluminium oxide left is called alumina.

Alumina has very high melting point 2348K.

Aluminium is extracted from alumina by electrolysis but electrolysis can only

be carried out in molten state so alumina is dissolved in molten cryolite

(NaAlF6) for electrolysis, some fluorspar (CaF2) is also added to this mixture to

further reduce the melting point.

Electro reduction of alumina to aluminium:

Aluminium can be obtained from alumina (purified bauxite) by electrolyticreduction method. This method was developed by Charles Martin Hall in

1886. This method is also called Halls electrolytic process. In this process:

(1) An iron tank lined from inside with carbon lining is used as the electrolytic both.

(2) The carbon lining acts as cathode (ve elechode)

(3) Anode consists of a number of carbon rods suspended into the tank.

(4) A molten mixture of alumina (Al2O3) in cryolite (Na3AlF6) is used as the electrolyte.

Cryolite (Na3AlF6) is added to alumina to:

Lower the melting point of alumina.

Make the electrolyte a good conductor of electricity.

Physical characteristics of Aluminium:

(1) Pure aluminium is a silvery white metal.

(2) It is very ductile & malleable. It has high tensile strength.

(3) Aluminium is a good conductor of heat & electricity.

(4) Aluminium is a light (low density) metal.

(5) Aluminium can be cast & welded.

Electrolytic reduction of alumina. A molten mixture of alumina, cryolite andfluorspar is electrolysed using graphite electrodes. Aluminium is obtained at thecathode.


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Uses of aluminium:

Some common uses of aluminium are:

(1) Aluminium is used to make electrical wires & cables for domestic/ industrial use.

(2) Aluminium is used to make domestic utensils.

(3) Thin foil of aluminium is used in packaging food materials, such as biscuits,

chocolates etc.

(4) Due to its low density, aluminium is used in construction industry.

(5) Aluminium powder is used in making paints & explosive & as a reducing agent in

metallurgy.

IRON:

Symbol: Fe

Atomic Number: 26

Atomic Mass: 56

Electronic Configuration:21482

NMLK

Most widely used metal.

It is second most abundant metal in earths crust.

It occurs in combined form in nature & it is not found in elemental form as it is very

reactive.

It is found as an oxide, carbonate & a sulphide.

The chief ore from which iron is extracted is called haematite.

It is mostly iron (III) oxide Fe2O3 mixed with some sand (Silicon SiO2)

Extraction of the Iron from Haematite:

(a) Concentration of ore: Crushed ore is washed with water to remove clay.(b) Calcination: The washed ore is heated in the absence of air.

During calcinations following things happen:

(a) Moisture is removed, carbonates converted to oxides.

(b) Ferrous oxide is converted to ferric oxide.

32Heat

2 OFe2OFeO4 +


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Reduction of Haematite to iron with carbon: Smelting

Iron is obtained by the reduction of its ore haematite (Fe2O3) in a big furnace called blast

furnace.

Furnace is narrow at the bottom.

Widens out in the middle.

Again narrows down at the top.

It is made from steel.

Inner regions are lined with fireproof bricks.

(Iron ore) is mixed with coke & limestone to form a mixture called the charge. It is

introduced into the blast furnace from the top.

blast of hot air is blown in through the base of the furnace , following reactions take

place.

(a) Coke combines with oxygen to form carbon dioxide.

C + O2 CO2 + Heat

Blast furnace for the extraction of iron. A mixture of iron ore, coke and limestone is fed

from the top of the furnace. Coke is converted into carbon monoxide, which reduces iron(III) oxide to iron. Limestone decomposes to give calcium oxide, which combines withsilica to form a slag.


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(b) Due to the intensive heat in the furnace limestone (CaCO3) decomposes to form

Calcium oxide & CO2.

CaCO3 CaO + CO2

(c) The carbon dioxide reacts with more coke to form carbon monoxide.

CO2 + C 2CO

(d) Iron (III) oxide present in the ore is then reduced by carbon monoxide to form liquid

iron. The molten iron trickles down & collects at the bottom of the furnace.

Fe2O3 + 3CO 2Fe + 3CO2

(e) Calcium oxide (flux) reacts with Silicon Dioxide (Sand) present in the ore as impurely

to form molten calcium silicates known as slag.

CaO + SiO2 CaSiO3 (l)

Molten slag is lighter than molten iron, it does not mix with iron & forms a molten layer

above the iron & protects iron from oxygen & prevents its oxidation.

Alloys:

An alloy is a homogenous mixture of two or more metals or a metal and a non metal.

Composition and uses of some alloys of copper

Alloy Composition Uses of properties

Brass Cu 60 80%

Zn 20 40%

Uses: Brass is used for decoration

purposes, for making many scientific

instruments, telescopes, microscopes,

barometers, etc.

Bronze Cu 80%

Zn 10%

Sn 10%

Uses: In making statues, cooking utensils and

coins.

German silver Cu 30 60%

Zn 25 35%

Ni 15 35%

It is silver white as silver, malleableand

ductile.

It is used for silver imitation. In making

ornaments and utensils and also for

decoration.

Gun metal Cu 88%

Sn 10%

Zn 1%

Pb 1%

It is used for making gears and bearings,

and gun barrels.

Bell metal Cu 80%

Sn 20%

It is used for csting bells.


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Composition and uses of some important alloys of iron

Alloy Composition Uses and properties

Stainless steel Fe 74%

Cr 18%

Ni 8%

Uses: For making cutlery,

utensils, ornamental pieces

and some other instrument

and apparatus.

Properties: stainless steel is

hard, tenacious and

corrosion resistant.

Nickel steel Fe 96 98%

Ni 2 4%

Uses: For making electric

wire cables, automobile and

airplane parts, watches,

armour plates, propeller

shafts, etc.

Properties: Nickel steel ishard, elastic and corrosion

resistant.

Composition and uses of some important alloys of aluminium


Duralium

or

Curalumin

Al 95%

Cu 4%

Mg 0.5%

Mn 0.5%

Uses: For aeroplanes,

spacecrafts, sea ships and

pressure cookers.

Properties: In strength, it is

as good as steel but it is

very light. It is hard,

corrosion resistant and

highly ductile.

Magnalium Al 90 95%

Mg 5 10%

Uses: For making light

instruments, parts of

machines and balance

beams.

Properties: It is hard and

tough.


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Composition and uses of some important alloys of lead


Solder Pb 50%

Sn 50%

Uses: Used for soldering

purposes.

Properties: It has alow

melting point.

Type metal Pb 75 80%

Sb 15 20%

Sn 5%

Uses: For making printing

type.

If one of the metals is mercury in an alloy then the alloy is said to be amalgam.

Carats: The proportion of gold in alloyed gold is expressed in carats.

Pure gold is 24 carats, The alloys commonly used are 9 carats 9 parts of gold in 24

parts of alloy or18 carats 18 parts of gold in 24 parts of alloy.

Corrosion:

When a surface of a metal is attacked by air water or any other substance around it, it is

said to corrode & the phenomenon is known as corrosion.

Rust: When iron is exposed to moist air for a long period of time, its surface acquires a

coating of a brown flaky substance called rust.

Rust is mainly hydrated Iron (III) oxide (Fe2O3. xH2O)

Metals(educationpoint.co.ccc)

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