Group 16 elements

7/31/2019 Group 16 elements

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Oxygen Page 1

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Group 16

OxygenAtomic Number=8

Atomic Weight=16

Configuration=1s2 2s2 2p4

Electronegativity=3.5

Oxygen Lavoisier. Oxygen means an acid producer. The products obtained by the

chemical combinations of O2 with non-metals like S, P, C etc on being treated with water

produces acid.

It exists to about 21% by volume, 23% by wt and 46.5% of earths crust.

Difference between O2 and other members of group 16:-

Oxygen is the first member of Group VIB in the periodic table. The properties of oxygen

differ with the other members because of the following:-

(i) Small size of O atom.(ii) Higher electro negativity of oxygen(iii) Absence of d orbital in the electronic configuration of O atom.

Members Periods At-no Config of valence shell

Oxygen 2 8 2s22p4

Sulphur 3 16 3s23p4

Selenium 4 34 4s24p4

Tellurium 5 52 5s25p4

The main differences are:-

(i) Physical state:- O2 is a gas while all others are solids(ii) Abundance in nature:- Max for oxygen. Abt-46.6% of earth.(iii) Atomicity:- O2 is diatomic. Other elements have a somewhat complex

molecular structure. S and Se occur as Se8 and S8 at room temperature.


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(iv) Oxidation state:- The various oxygen states of O2 are: (a) +2 in OF2, (b) -2 ingeneral, (c) -1 in peroxides. The oxidation no of all other members is both

+ve and ve, but majority of them in +ve state.

(v) Maximum covalency:- As d orbital is not available in oxygen atom the maxcovalency exhibited by it is 2. But due to the presence of d orbital the othermembers of the group exhibit a max. covalency of 6 upto Se and 8 upto rest.

This explains why SF6 is formed but O cannot.

(vi) Existence of H-bond:- Due to high electronegativity and structure size of itsatom, H-bond plays an important role in the properties of the compounds of

O. Due to H-bonding, the b.p and m.p of H2O are much higher than other

members whereas instead of H-bonding vanderwalls forces are present

which increases down the group with increase in molecular weight.

(vii) Nature of hydrides:- The hydride of O2i.e water is a colorless, odorless,neutral liquid but other hydrides are gases, combustible, poisonous, having

bad odor and acidic nature.

(viii) O2 is more electronegative and hence more ionic in its compounds.(ix) O2 can use p orbitals to form strong double bonds. This tendency weakens as

atomic no increases.

Preparation:- O2 is prepared by heating a mixture of potassium chlorate and

manganese dioxide, when KClO3 is decomposed to give KCl and O2. MnO2 acts as a

positive catalyst in this decomposition and remains unchanged after the completion

of the reaction.

Precautions:-

(i) Pure MnO2 free from C and Sb2S3 must be used, otherwise there maybe explosion.

(ii) Half of the test tube should be filled for easy escape of O2.(iii) Slow and uniform heat should be supplied.(iv) The test tube must be kept with a slightly downward incline.(v) The end of the delivery tube should be kept above water to prevent

entry of water in the hot test tube.


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Function of MnO2:- MnO2 acts as a +ve catalyst in this reaction. It brings down the

decomposition temperature from 630 C to about 200-250 C and O2 evolfves more

rapidly without the formation of KClO4.

Properties:-

[A] PHYSICAL PROPERTIES:-(i) Colourless, odourless, tasteless neutral gas.

(ii) Little heavier than air.

(iii) Slightly soluble in water (4%)

(iv) MP=-218 C, BP = -183C(v) Supporter of respiration(vi) Paramagnetic(vii) It can be liquidified by cooling under pressure to a pale blue liquid.

[B] CHEMICAL PROPERTIES:-

(1) Allotropy:- O2 exhibits allotropy O3. Gaseous O2 is diatomic but ozone is

triatomic. They are 2 different forms of the same element.

(2) Chemical activity:- Very active element combines directly with most of the

elements except the halogens and the inert gases. Its chemical activity is enhanced at

high temperature and in presence of a catalyst.

(3)Combustion: Oxygen is not combustible but a supporter of combustion. The

combustible substance is oxidized by oxygen producing heat and light during

combustion.

(4) Formation of Oxides: -

a. Reaction with non-metals in formation of acidic oxides:-Non metals like, C, S, P on

being ignited in oxygen burn with bright flames and combine with O2 producing acidic

oxides. This class of oxides react with bases to form salts and water and produce acids

when dissolved in H20.

b.Formation of neutral oxides:- H2 burns in O2 with a blue-flame to form water which is

a neutral oxide.2H2 + O2 = 2H2O

N2 combines with O2 at 3000C in presence of electric spark to form nitric oxide which is

also a neutral oxide.

2N2 + O2 2NO.

Oxygen does not combine directly with Cl2, Br2 or I2.


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(a)Reaction with metals :- (i) Formation of basic oxide :-The alkali metals like No, k etc. and the alkaline earth metals such as Ca, Sr etc.

combine with O2 directly producing basic oxides [These oxide are generally ionic

compounds with high m.p & b.p]

Heated Na burns in O2 with golden yellow flame of form Na2O, with excess of O2Na2O2 is formed Na2O dissolves in water to produce NaOH.

4Na + O2 = 2Na2O, 2Na2O + H2O = 4NOOH.

2Na + O2 = Na2 O2. BaO. BAO + H2O = Ba(OH)2

K burns with a violet (lilac) flame to produce K2O, with excess of O2, K2O2 is

formed

4K + O2= 2K2O, K2O + H2O = 2KOH

2K + O2 = K2O2

2Ca + O2 2CaO, CaO + H2O = Ca(OH)2

2Mg + O2 2MgO (feebly basic)

Red hot fe on being introduced into a jar of O2 turns bright and combines with O2

to form ferrosoferric oxides

3Fe + 2O2 = Fe3O4

Wake electro positive metals like Cu, Ag etc on being heated are gradually

converted to their oxides

2Cu + O2 = 2CuO, 4Ag + O2 = 2Ag2O

(4) Formation of amphotoric oxide :- Metals like Al, Zn, Sn, Pb produce.

Ampuoteric oxide. These oxide react both with the acids as well as with the

alkalis to form salts d water

4AL + 3O2 = 2Al2O3 6 2 3 2 2

2Zn + O2 = 2ZnO 2 2 . O2 cannot combine directly with pt, Au to form their oxides.

(*) O2 means an acid producer, but sometimes the name is misnomer (i) S, C, P

acidic oxide produces acid but with Na, Ca, K basic oxide of H2O, NO neutral

(5) Oxidising Property:- O2 is a strong oxidizing agent it oxidises a substance by

combining directly with it or by increasing the proportion of electronegative element in

the substance


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(i) 2NO + O2 = 2NO (broun fumes)

(ii) 2H2SO3 + O3 = 2H2SO4

(iii)4FeSO4 + 2H2SO4 + O2 = 2Fe2 (SO4)3 + 2H2O

(Colourless) (Yellow)

(iv) 4FeCl2 + 4HCl + O2 = 4FeCl3 + 2H2O(v) 2SnCl2 + 4HCl + O2 = 2SnCl4 + 2H2O.

(vi) 2Cu2Cl2 + 4HCl + O2 = 4CuCl2 + 2H2O

(vii) 2SO2 + O2 2SO3 (contact process)

(viii) 4NH3 + 5O2 4NO + 6H2O

(ix) Deacons process:-

4HCl + O2 2H2O

(6) Reducing action: - 2F2O2 = 2OF2 (oxygen di flouride)

F2 O2. So. Oxygen looses electrons to F.

Thus Oxygen is oxidized by fluorine

2F + 2e 2F- (reduction) , O 2e O+2 (Oxidation)

O+2 + 2FD- OF2

(7) ABSORBANTS OF O2 : - (i) AlK. SOLn of potassium pyrogalla absorbs oxygen and the

colour of the solution turns broom.

(ii) Ammoniacal Cu2Cl2soln.

Absorbs O2& the colour of the sloln. turns blue

* TESTS FOR OXYGEN

(i) A glowing piece of wood bursts into test when it is introduced into a jar of O 2. By this

test O2 may be identified from all other gases other than N2O.

(ii) Colourless NO when comes in contact with O2 brown fumes of NO2 are produced.

2NO + O2 = 2NO2 (brown fumes).

(iii) Alkaline. Pot. Pyrogallate

brown

* USES: - (i) Welding cutting Only hydrogen & only acetylene flames

(ii) Artificial respiration (iii) Rocket jet fuel

(iv)Uses in the L.D process for the manufacture of steed O2 oxidises the impurities of

cast iron

* Oxygen has 3 naturally occurring isotopes:-

4500C, Pt Cat

Pt Cat

V2O5

7500C

Cu2Cl2

400 5000 0C


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Isotopes

is radioactive

Abundance .%

.%

.%

in nature

* Reaction of oxygen with hydrocarbons & CS2 :-

CH4 + 2O2

CO2 + 2H2O

2C2H2 + 5O2 4CO2 + 2H2O

CS2 + 3O2 CO2 + 2SO2

C6H12 + 6O2

6CO2 + 6H2O + energy

Periodic Trend:- From left to right on moving in a period the nature of the oxide changes

from very strongly basic to amphoteric to very strongly acidic .

Na2O NaO Al2O3 SiO2 P4O10 SO3 Cl2O7

Strongly Basic amphot weakly acidicbasic eric acidic strongly acidic

In contrast in moving down the group the basic character of oxides increases

B2O3 Al2O3 Ca2O3 In2O3 Tl2O3

Acidic Amphoteric Basic

Metallic oxides are generally basic while non- metal oxides are acidic.

N2O NO N2O3 N2O4 N2O5

Neutral Weakly acidic Acidic Strongly Acidic

Acidic character increases with increase of oxidation no

OXIDES

An oxide is defined as the binory compound formed by the union of O2an other

element (except)

(i) Basic oxides:- Basic oxides are generally the oxides of metals which react withacids to produce salt water en Na2O, CaO, CuO, Fe2O3

CuO + 2HCl = CuCl2 + H2O

NgO + H2SO4 = MgSO4 + H2O

Basic oxides if solution in water, produces soluble base or alkali.This solm.

Turns red litmus blue& gives OH- as anion

4Na + O2 = 2Na2O ; Na2O + H2O = 2NaOH

NaOH Na+ + OH-


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The basic oxide contains oxygen atoms with electron pairs avaitable for

bonding. When the oxygen is linked to a strong electro + ve element, the

bond beth.Them become, polar and O atom acquires O large negative charge.

As the density of this ve charge inareases, the ability of oxygen for donating

the lp of electrons also increase and thus the basic character of the oxidesincreases and thus the basic character of the oxides increases As cs is more

electro + ve than Li CSO2 is more basic than LiO2. For the same reason Bi2O3

is more than P2O3.

Soluble basic oxides give OH- ions in aq solm as O H bond is left

polar than the bond betn oxygen and the metal in an oxide. The strong polar

bond betn. The metal & oxygen becomes weaker in a polar solvent like water.

This because the electron gativityidd. Betn the central element & oxygen is

grater than betn (oxygen & H2)

H O Mg O H + nH2O {Mg (H2O)x]+2 2OH-

(ii) Acidic oxide:- The oxides of non metal which metal with bases to producesalt & water are known as acidic oxides. Such oxides if water to form acids e.g

so2, co2, p2o5, SiO2, B2O3etc

CO2 + 2NaOH = Na2CO3 + H2O. SO3 + Na2O = Na2SO4

CO2 + H2O = H2CO3 , SO2 + H2O = H2SO3, Cl2O + H2O = 2HOCl

The acidic oxide from which the acid is produced on treatment with water is called the

anhydride of the acid.

Metallic oxides containing larger amount of O2beha- ve like acidic oxide. In fact as the

own no. of the metal increases, the acidic property of the metallic oxides also increases,

I.e why MnO is basic Mn2O3 is amphoteric, Mn2O7 is strongly acidic

(Permanganic acid)

CrO3 + 2KOH = K2CrO4 + H2O

Acidic oxides are acceptors of tone pair of electrons. The highly electromegative central

atom bounded to O atom is acceptor. The acceptance ability of the central atom is

further enhanced becor of the with drawl of electrons by the more electro-ve O atom.

Sometimes atom of low electronegativity such as Mn or Cr becomes highly electro-ve&

thus O acquires the e acceptance ability when a no. of O atoms are attached to it. The


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electron acceptance ability increases as O pulls the b-p more towards itself. Thus, SO3>

acidic> SO2 is atoms in SO3 is a better acceptor of electrons)

Acidic character increases with the increase of, the number of O atoms attached to the

central atom.

(iii) Amphoteric oxide:- The oxide which octs as both basic & acidic oxide. React withstrong acids as well as strong alkalis to yield salt & water.

e.g 2no.Smo, pbo, Al2O3 etc.2nO + H2SO4 = 2nSO4 + H2O

2nO + 2NaOH = Na22nO2 + H2O.

If the partial negative charge on the O atom of an oxide is in betn that of a typical acidic

& basic oxide it will exhibit amphoteric behavior.

(1) Basic character

when its bonded O atom acts as donor to the central atom of an

acidic oxide which acts as acceptor.

2n O: SO32nSO4(2) Acidic behaviour when its central atom acts as acceptor when comes in contactwith the bonded oxygen atom having high ve charge of a basic oxide

Cao: 2no ca2no2.In aq-med. Amphoteric oxide may give rise to both (H3O)+& OH- depending upon the

nature of reactants if the diff. in electronegativity between O-H & M-O is comparable

then there is equal chance of release of H3O+& OH-

(iv) Neutral oxide:- The oxide which reacts neither with the acid nor with the base to

produce salt is called neutral oxide. The do not react with water to produce acidic or

basic solution. E.g H2O, N2O, NO, CO. All neutral oxides are the oxides of non-metals.

Although water is classified as neutral oxide it can act both as acid & base

according to Bronsted Lowry idea of acids & bases.

H2O + H2O H3O + OHAcid base2 acid2 base,

(v) Peroxide:- An oxide which gives H2O2 on treatment with cold and dit mineral acidsand which contains peroxo bond [- 0 0 -] is known as peroxide. The peroxide of an

element contains more oxygen oxide.

e-g Na2O2, BaO2. H2SO5 + H2O H2SO4 + H2O2(caros acid)

BaO2 + H2SO4 = BaSO4 + H2O2


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Na2O2 + 2HCl = 2NaCl + H2O2

* Pbo2& Mno2 are known as dioxides & not peroxide because (i) they do not yieldH2O2 on being treated with cold & dil mineral acids (ii) They do not contain any perowlink (-O O-) in the molecule but the O atoms are attached to the metal covalent by =

bonds.

Mno2 + 4HCl = MnCl2 + Cl2 + 2H2O

2Mno2 + 2H2SO4 = 2MnSO4 + O2 + 2H2O

(vi) Mixed oxides:- The oxide which is formed by the union of 2 oxide of same metal in

diff. valency state, is called a mined oxide. On being reacted with acids they yield

minture of salts corresponding to metal in diff. valency state. e.gFe3O4 (FeO. Fe2O3), pb3O4 (2pbo + pbo2) Mn3o4 (2Mno + Mno2)

Fe3O4 + SHCl = 2FeCl3 + FeCl2 + 4H2O

Pb3O4 + 4HNO3= pbo2 + 2pb(NO3)2 + 2H2O

(vii) Poly oxide:- An oxide which contains more O2 than either the acidic or basic oxide

but does not produce M2O2 on being treated with dil. Mineral acids is called poly oxide.

e.g Mn2O7, MnO2, Pbo2(viii) Sub oxide:- There are some oxide in which the element combined with oxygen is in

unusually low oxidation state. C3O2 (carbon suboride). O = C = C = C = O

(ix) Super oxide:-Alkali metal like Na, K, Cs, Rb form a type of oxide which contains a

lattice of CaC2 type in which the anionic species is ion. The anion has the structure

[:O O] involving a single bond & a 3- electron bond betn 2 oxygen atoms. All super

oxides are paramagnetic & coloured)[O2]-has 17 electrons:-

1 1 2 , 2 , 2 2

,Increasing energy

e.g lio2& NaO2 yellow, KO2arangered, RbO2brown

OBa , Na O Na [O O]2- ion

O

O O

Mm , Pb they produce Cl2& O2 on being treated with cono& hot HCl &

O O H2SO4


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Cso2 arrange. Ca(o2)2Superoxides are even stranger oxide sing agents than perwxides. They differ

from peroxides in stricture & reactivity.

While peroxides liberate H2O2 with cold dil. Acids. Super oxide liberate O2, for

which they are strong oxidizing agents4KO2 + 2H2SO4 = 2x2SO4 + 2H2O + O2

With ice cold water they form O2 as well as breathing masks co2 it produces

O2&romeves CO2. Both functions are imp. In life support systems

4KO2 + 2CO2 = 2K2CO3 + 3O2

*generally large atoms or ions form weaker bond than small ones. The peroxide &

superoxide ions are large and it is noteworthy that the stability of the

perosides&superxides increases as the metal ions becomes larger. This shows that large

cations can be stabilized by large anions, since if both ions are similar in size the C.N will

be high, and this gives a high lattice energy

* There are 3 adv. Of using O2 in the kaldo d l.D process of converting pig iron to steel

than using air in the Bessemer process:-

(i) The conversion to steel is quicker

(ii) Large ingots of pic iron can be used

(iii) The metal does not form nitrides, which can ocour when air is used

* Oxygen (O2) is paramagnetic & therefore contains unpaired electrons. The structure

on the basis of MOT is

1 1 2 2 2

2 2

2

2

* Liquid O2 is pale blue in colour, the solid is also blue. The colour arises from electronic

transitions which excity the ground state (a triplet state) to a singlet state. This

transition is forbidden in gaseous oxygen. In liquid or solid O2 a single photon may

collide with 2 molecules simullancously& promote both to excited states. Absorbing red

yellow- green light, so O2 appears blue. The origin of the encitedsirglent states in O2

lies in the arrangement of electrons in the antibonding2 and

2

Molecular orbitals:-

Second excited state singlet /

(electrons have opp. Spins)

First ercited state singlet 92 (electrons paired)


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Ground state triplet O (electrons have spins)

Singlet O2is ercited& is much more reactive than normal ground state triplet O2. Singlet

O2 can be generated photo chemically by irradiating normal O2 in presence of a

sensitizer ( flour escain, methylene blue or some polycliccompounds) charieally it can

be made as:-

H2O2 + OCl- O2 (singlet) + H2O + Cl-

Singlet O2 can add to a diene in the 1,4 positions rather like a Diels Alder reaction.

* Oxygen, being smaller in size, is capable of forming multttiple bonds with itself f & other which lead to its following abnormal charocteristies:-

(i) Its diotamic d gaseous nature; other elements exist as 8 membered ring or zi zag

chain structures & are solid in nature.

(ii) Its low b.p, m.p & density.

(iii) Multiple bonds are shorter, the o o bond dist in o2 is less (1, 21)which leads tohigh b.E & hence more energy must be supplied to break the o o bond thus, O2 is inert

although it is the second most electro-ve element (F F b. E is much less &hance everyreactive lp.lp repulsion on the two fatonrs)(iv) oxide ion is not easily polasised (small ion with high charge density) (fajansruls), so

it called a lard ion while the remainder ions are called soft ions so must oxygen

compounds are ionic

* Prep of O2:-

2MnO2 + 2H2SO4 = 2MnSO4 + 2H2O + O2

4KMnO4 + 2H2SO4 = 4MnSO4 + 2K2SO4 + 6H2O + 5O2

2K2 Cr2O9 + 8H2SO4 = 2K2SO4 + 2(r2(SO4)3 + SH2 O 1 3O2

Ozone (O3)

(I smell) Schon bein.Ozone is an allotrope of oxygen with molecular formula O3.

CH2 CH2

CH CH +

singlet O2


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Formula O3

Due to irradiation of O2 with u.v light.

O2 2 (a ctivated) ( = 220 290 nm)

O2

O2

O3

O

PREPARATION

(i) Silent electric discharge through O2, O3 is prep. by passing silent electric discharge

through pure &driy O2.

3O2 2O3 241 Kcal.

This conversion of O2 to O3 is a reversible reach and the forward reaction is

endothermiaSo according to le chateliers principle, the increase of temperature should

the forward reaction& thus the yeid of O3 should increaseBut as O3 is very unstable tends to decompose into O2 even at room

temperatureThis decomposition is accelerated by the increase of temperature during

ordinary electric discharge much heat is produced along with the electric spark. If O2 is

subjected to this ordinary electic discharge, the produced ozone will decompose to give

oxygen by the gen- of heat.

If the two electron des are covered by an insulating

material such as glass & connected to the terminals of an induction material such as

glass & connected to the terminals of an induction coil, silent electric producing e-spark& heat. Thus the decomposition of the produced O3 is considerably retarded & hence O2

is subjected to silent electric discharge.

(2) Ozoniser:-Ozoniser is the apparatus used for preparing ozone from O2 by passing

silent electric discharge time it.

(i) Siemens ozoniser7-10% ozonc (tinfoil)(ii) Brodies ozoniser 20% ozone (pt wire & dil H2SO4)(iii) Siemen Halskeozoniser

large scale production:-

* Preparation of pure ozone from ozonized oxygen:-

(i) The ozonized O2 is condensed to give a deep blue liquid which contains liquid O2&

O3.

(ii) The blue liquid is subjective to fractional distillation O2 is more volatile than O3.

Evaporates first& liq. O3 is left behind.


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(iii) This liquid O3 is then very carefully vaporized when pure O3 is obtained as a deep

blue gas. This purification should be carried out with extreme care as liquid O 3 is highly

explosive

(*) Conditions for better yield of O3:-

(a) Temperature should be low. Around 273 k is maintained(b) Sparkless discharge is passed (iii) O2 should be pure & dry (dark)

Properties

[A] Physical Properties:-

(i) O3 is a pole blue gas (diamagnetic) having a fishy smell.

(ii)It turns to a dark blue liquid on condensation liq. O3 is highly explosive

(iii) O3 is more soluble in water than O2. It is also soluble in CCl4, CS2, CH3COOH etc. Due

to its high solubility in turpentine, turpentine is used as an absorber of O3.

(iv)Condenses to violet black solid (m.p = 80.6 k)

(v) Poisonous in nature produces headaches in small does.

(exposure to 1ppm must be avoided)


(i) Stability:- when O2 is converted to O3 energy is absorbed 3O2 2O3 241

Kcal O3 contains more energy than O2 A consequently it is less stable & much active.

Even at ordinary temp O3 decomposes slowly. Its decomposition becomes repid athigher temp (2000C). The decomposition of O3 is accelerated by finely divided Pt, Ag2O,

MnO2, dust particles etc. At 3000C O3 is comp. decomposed to give O2.

2O3300

0

3O2 + heat(2) Oxidising property:- As O3 contains more energy than O2, it is more active &

vigorous oxidizing agent than O2, it is because of the evolution of nascent oxygen by its

spontaneous decomposition Even at ordinary temperature O3 = O2 10. This nascent O

is responsible for the superior oxidising properties of O3.

There are 2 classes of oxidationreaction by O3:- [A] In which one molecule of O2

is given off for every molecule of O3 used in the reaction:-

(i) One of metals:- most metal are oxidesed to their corresponding oxides by O3

(a) 2Hg + O3 = Hg2O + O2 (dissolution)


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Due to formation of Hg2o, Hg loses its mobility &molalliccusture& sticks to the glass

when comes in contact with O3. This is called bailing of

Hg. The meniscus can be

(b) 2Ag + O2warmed Ag2O + O2 regained by shaking (brown layer) it water which

dissoues Hg2O

Ag2O + O3 aAg + 2O2 (Reducing action).(iii) Oxidation of compoundsi:- (a) Black pbs white pbso4.

Pbs + 4O3 = PBSO4 + 4O2

Similarly, cus&zns are converted to cuso4& znso4.

(b) colourlesssolm. Of acidified Pe+2 salts are osidised by O3 to yellow Fe+3 salts.

2FeSO4 + H2SO4 + O3 = Fe2(SO4)3 + O2 + H2O

2FeCl2 + 2HCl + O3 = 2FeCl3 + H2O + O2

(C) Colourless meutral or acidified som of KI or NaI is oxidized to free I2& the solm

turns broom.

Necutral:- 2Ki + O3 + H2O = 2KoH + I2 + O2

Acidified:- 2KI + O3 + 2HCl = 2KCl + I2 + O2 + H2O

* Ki is not oxidized to I2 by O3 in presence of FeSo4, while H2O2 can oxidize Ki even in

presence of FeSO4

(d) Mi\oist S, P & I2 are oxidized to their corresponding higher axy acids

I + 3O3 + H2O = H2SO4 + 3O2

2P + 503 + 3H2O = 2H3PO4 + 5O2

I2 + 5O3 + H2O = 2HIO3 + 5O2

(e) O3 oxidises NaNO2& NH4NO2 to the mitrates


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NaNO2 + O3 = NaNO3 + O2

NH4NO2 + O3 = NH4NO3 + O2

* Oxidation of metalloids:-

(i) 2Sb + 5O3 + 3H2O = 2H3 SbO4 + 5O2

(ii) 2AS + 5O3 + 3H2O = 2H3SAO4 + 5O2

(f) Halogen acids Hologens:-2HCl + O3 = Cl2 + O2 + H2O

2HBr + O3 = Br2 + O2 + H2O

(g) (i) H2S + 4O3 = H2SO4 + 4O2

(ii) 2K42 6O3 + H2O = 2K33 2 + O3Pole ferocyanide pot fericyanide

(iii) 2 K2MnO4 + O3 + H2O = 2KMnO4 + 2KOM + O2

(green) (pink)

(b) Ozone molecule as a whole is used up for oxidation.

(i) 3SnCl2 + 6HCl + O3 = 3SnCL4 + 3H2O

* O3 is netural towards litmes B.P of O3 = - 1120C

Excepting few reactions O2 is evohed in all other oxidation reactions carried out by

ozone. As the oxidation. No brought about in these reans but one oxygen atom of O 3 is

resuced by deoreasing its oxidation no form O to 2, while the other O2 atom suffers no

change

22 4

2 4 3 0 2 3

2 43

2 2 2


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(3) Reaction with peroxides:-Reaction of O3 with BaO2& H2O2 results in their mutual

redn with the evolution of O2. BaO2 is reduced to BaO& H2O2 is reduced to H2O.

BaO2 + O3 + BaO + 2O2

H2O2 + O3 = H2O + 2O2

The oxygen of the peroxo group is oxidized of free O2i.c form -1 to 0 & one atom of O3 is

reduced to BaO from 0 to 2 while O2 fO3 remains unattered. Oxidation

1

2 0 2 2 2 2

This prove that O3 is a powerfull oxidizing agent than H2O2.

(4) Bleaching Property:- O3 liberates nascent O which a oxidizes indigo & other

colouring matters into colourless compounds. Litmus paper becomes colourless whenexposed to an atomosphere of O3

(5) Formation of addition compounds:- With unsaturated organic compounds

consisting of = or = bonds O3 farms addition products called ozonides

CH2 = CH2 + O3 H[inert solvent like CH2Cl2, CCl4 at low temp = 195 K]

H C C H + O3Rubber contains unsaturation & so it io readily attacked by O3& as a result elasticity of

rubber is lost (*) O3 is used as a disinfectant & to purify drinking H2O. Its adv. Over Cl2 is

that is avaids unpleasant smell & taste of Cl2

(*) TESTS FOR OZONE:- (i) O3 is identified by its strong fishy smell.

(ii) A filter soaked in KI & starch som.Turns blue when brought in

contact with O3. O3 first oxisises KI to give free I2 and this free I2 reacts with starch

producing blue colour.

2KI + O3 + H2O = 2KOH + I2 +O2

Starch + I2 Blue colour

Red


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Oxygen Page 17


H2O2, Cl2, NO2etc also respond to this test

(iii) O3 turns benzidine paper brown &trimethyl base paper violet.

(iv) A drop of Hg when brought in contact with O3, its mobility & metallic lustue are lost

& it sticks to the glass

(v) It does not decolourise KMnO4 or K2Cr2O7

(*) Uses of O3:-

(i) As germicide & disinfectant in sterilising water

(ii) For bleaching oils ivaryetc

(iii) as an oxidation agent & In prep. of KMnO4

(iv) In destroying bad odours from cold storage, slaughter louses etc.

(*) Structure:- O3 is angular & the angle beth the 3O atoms is 1160491 301. The O Ob.d in O3 is 1.278 OO3 . Single O O b.d is 1.49 & O = O is 1.21, it is apparent thatO O bond is O3 must have considerable double bond character & it is a rhesonance

hybrid of the following:-

(*) COMPARISON BETWEEN OXYGEN AND OZONE:-

Oxygen Ozone

1. Colourless & odourless gas 1. Pale blue gas having fishy smell.

2. Absorbed in alk pot pyro gallate solbrown. 2. Abosonbed in terp entire

3. Does not attack Hg. 3. Hg in contact with O3 loses its mobicity&


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Oxygen Page 18


metallic custure Hg2O formation.

4. Stable but at high temp decomposes to give

nascent O.

4. At 3000C, decomposes to give O3 = O2 + O.

Decomp is accelerated by HnO2, Ag or pt

5. Does not effect rubber 5. attack rubber at ord temp & as a result it

loser its elasticity

6. Cannot oxidize pbs to PbSO4or KI Solm 6. Can oxidize both PbS + 4O3 = PbSO4 + 4O2

2KI + H2O + O3 = 2KOH + I2 + O2

7. At 4500C in presence of pt cat. Oxidizes So2 to

SO3.

2SO2 + O2

2SO3

7. At ord temp it oxidizes SO2 to SO3

3SO2 + O3 = 3SO3

* Destruction of O3 layer in atmosphere:- CFC & NO

From car exhausts

CF2Cl2 + h CF2Cl + ClCl + O3 ClO + O2ClO + O3 Cl + 2O2

* STRUCTURE OF O3:- The central O atom uses sp2 hybrid orbitals to bond to the

terminal O atoms. The central atom has one lp, and the terminal O atoms have 2 lps. This

leaves 4 electrons for bonding. The P2 atomic orbitals from the 3 atoms form 3

delucalised m. os covering all 3 atoms. One MO is bonding one non-bonding & one

antibonding. The 4 electrons one delocalized bond to the molecule in addition to 2

bonds. Thus the bond order is 1.5 & the system is decribed as a four-electron 3 centre

bond.

* The dark blue colour of O3 is due to intense absorbtion of red light ( 557 nm & 602

nm). It also absorbs strongly in the uv region ( 255nm).

* 2KOH + 5O3 2KO3 + 5O2 + H2OPot. Ozoxide KO3 is an orange red coloured solid contains the paramagnetic O3 ion


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Oxygen Page 19


SULPHUR (S)

Natural sources

Well distributed in nature both in the free state& well as in combination, such as

sulphides & sulphates of many metals:-

(i) FeS2 (Iron pyrites or fools gold)

(2) copper pyrites (cu2S, Fe2S3)

(3) Galena (pbs) or lead glance

(4) zinc blend (zns)

(5) ciypsune (caSO4. 2H2O)

(6) Barytes (BaSO4)

(7) Kiesserite (MgSO4, H2O)(8) MoS2 (Molybdenite)

(9) Cinnabar (gas)

EXTRACTION OF SULPHUR:-

Deposites of free S occur particularly in the volcanic regions

Sicilian process:- Mainly used for working up the Italian deposits.

Purification:- Impure S molten S Vapours generated

S melts1200 as yellow powder pure S is molulded (flowers of sulphur)

(roll of sulphur)

From the underground deposits (American process):- The underground deposits of s are

melted by pumping superheated water (1700C) under a pressure of 8 10 atm & a balst

of hot compressed air at pressure of abt. 35 atm through the s beds. The molten S is

then bloom out through with the compressed air

From natural gas:- Recovering of S from the natural gas includes separating-out H2S by

absorption into mono ethanol annulene& then converting H2S into S by the following

sequence of reactions:-

2 12 2 18 8 2 A certain amount of SO2 is formed which can be removed as:-

2H2S + 3O2 2SO2 + 2H2O


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Oxygen Page 20


2H2S + SO22 3

303

3

8 8 2 2

From spent iron oxide:- Obtained as a by-product in the manufacture of coal gas. It

consists of mainly Fe2S3. This spent iron oxide is left is exposed to sir when free S is sep

from it with the formation of Fe(OH)3

2Fe2S3 + 3O2 + 6H2O = 6S + 4Fe(OH)3

From sulphide ores:- A large amount of SO2 is obtaind as a by. Product during the

roasting of sulphide ores of metals like pb, Cu, znetc

Na2SO3 + SO2 + H2O = 2NaHSO3

2NOHSO3 = Na2SO3 + SO3 + H2O

SO2 + C = COS + S

From alkali wastes:-Cas + H2O + CO2 = CaCO3 + H2S

2H2S + O2 (limited) = 2H2O + S* ALLOTROPIC FORNS OF SULPHUR:- Like many other non-metals, s also exlibts the

phenomenon of allotropy. It exists in a number of allotropic forms which possess

different physical characteristics:-

[A] CRYSTALLINE ALLOTROPES:- (i) Rhombic or Octahedral or & sulphur:- (i) When roll

sulphur is dissolved in CS2 and the solm is slowly evaporated transparent yellow

octahedral crystal of rhombic sulphur are abt.

2. At ordinary temp, this is the most stable & common form of S. All other allotropic

forms of S are gradually converted to this form.3. Rhombic S is lemon yellow crystalline & the crystal are octahedral

4. Its m.p is 1140- 50C & b.p = 4450C. its density is 2.07 gcc

5. It is readly soluble in CS2, hot chloroform & C6H6

6. Non-conductor of heat & electricity

7. It exists as SS molecule. The 8 S atom in S8 molecule form a puckered ring, connected

to one another by single covalent bond.

* Conversion of & - S into S:- [The two sulphurs are called enantiont ropic

substantces]

95. 5

95. 5

(Transition temp) = 95.50C


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Oxygen Page 21


[B] Amorphous sulphur:-

(i) plastic sulphur:-

1. It is also called - sulphur & does not have sharp melting point.

2. Plastic sulphur is a brown coloured clastic solid & is regarded as a super cooled

liquid.3. Its density is 1-95 g/c.c

4. Plastic sulphur in insoluble in water as well as in CS2

5. It is anstable& at ordinary temp, or even standing it gets converted to rhombic

sulphur

6. itunterains long intervened zig zag chains of S atoms. These chains are formed by

opening SS chains

[ Supercolled liquid:- A liquid which due to rapid colling below its m.p had no time to

sette in orystallim form]

ii. Mick of sulphur:- By boling flowers of S with water & milk of lime, when a red

coloured som. Of CaS5 is obatainedvarityprecipitetes out which is called milk of sulphur

* CaS5 + 2HCl = CaCl2 + H2S + S Its density is 1.82 g/cc. Insoluble in H2O but soluble in CS2. This variety tends to revert

to the rhombic variety if kept over a long period

iii. Colloidal sulphur:- (a) obtained as a milky suspension by passing H2S through a

saturated solm of SO2

(b) By adding conc. H2SO4 to a saturated solm of sodium thiosulphate. On long standing

C.S changes soidiumthiosulphate. On long standing C.S changes to normal

(b) Na2S2O3 + H2SO4 = Na2SO4 + SO2 + H2O + SForm (a) SO 2HS 2HO S * 3Ca(OH)2 + 128 2CaS5 + CaS2O3 + 3H2O

Cal pentasulphide cal thiosulphate2CaS5 + CaS2O3 + 6HCl 3CaCl2 + 3H2O + 125

(Mainly used in medicines)


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Oxygen Page 22


PROPERITES OF SULPHUR:-

[A] PHYSICAL PROPERTIES:-

i. Pale yellow crystalline solid

ii. Britlle& cannot conduct heat & electricityiii. Enhibits allotropy

iv. Insoluble in H2O but soluble in CS2, C6H6etc plastic S in insoluble even in CS2

* Action of heat on sulphur:- S echibits remarkable changes when it is heated gradually

110 1190C S melts to a clear mobile yellow liquid120 1600C Instead of becoming more mobial it becomes thicker & darker to a deeporange liquid

160 1800C Becomes almost immobile & ciscous2300-C Colour becomes block & its viscosity increases230 onwards becomes mobile again444-60C begins to bail giving off yellow vapours when boiling S is allowed to cooldown slowly reverse change occurs

Explanation: Molecules of S are composed of 8 atoms arranged in a closed puckered

ring. Just above its m.p. such type of molecules can easily slip over the other and so the

liquid possesses mobility. At above 1600C rapture of the ring structure begins and is

completed at 2300C when the ring structures are converted to large chains of S-atoms.

This change is exhibited in deepening of its color. On more chains being formed &

getting tangled up, the viscosity of the liquid increases and it loses its mobility. When

temperature is further increased, the larger chains break up into smaller fragments and

as a result the mobility of the liquid increases again.

The liquid becomes darker in color, till at 444.60C it

takes the form of a black liquid & begins to boil giving off a yellow vapour.

At still higher temperatures, the vapour of S8 molecules dissociate forming S6,

S4& S2 molecules. At 10000C, the V.d of S correspond to S2& above 22000 monoatomic

molecules of S are produced. S2 molecule is paramagnetic & blue coloured like O2& has

similar bonding


Sulphur is inert at ordinary temperature but when it is heated, it becomes very active &

reacts with a large number of elements


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Oxygen Page 23


1. Action on Nonmetals:- When S is strongly heated in air or O2, it combines with O2 to

form SO2, with a trace of SO3

S + O2 = SO2, 2S + 3O2 = 2SO3

(b) Action on hydrogen:- When mixture of H2& S is passed even red hot pumice stone or

when H2 is passed through molten S, H2S is producedH2 + S = H2S

(c) Action on Cl2:- When Cl2 bubbled through boiling S, Sulpharmonocholoride an

orange liquid is produced 2S + Cl2 = S2Cl (orange liquid)

(d) Action on phosphorus:- S reacts with P at ordinary temp yeicding phosphorus penta

sulphide

P4 + 10S = 2P2S5 also P4S3 (tetraphosph 10000C onus trisulphide)

(e) Action on carbon:- C + 2S(Vapour) = CS2 (red out)

(f) Action with steam:- 3S + 2H2O 2H2S + SO2(reverse of reaction both H2S & SO2)

2. Action on metals:- Heated metals like Cu2Zn, Fe, Na etc react with S yielding the

corresponding sulphides.

CutS =CuS (black)

FetS = Fes (black)

Na or K catches fire as soon as it it comes in contact with sulphuric vapour

2Na + S = Na2S

At ordinary temp, Hg combines when S is powdered & titrated with Hg yielding HgS

(cinnabar)

Hg + S = HgS

3. Action on mineral acids:- S does not react with dil. HNO3, dil- H2SO4 or cons HCl

6 O 42H2SO4 S 3SO4Chat& H2O [Comproprtionation]5 0 66

3

2 4

& 46 2 2 2

4. Action on alkali:- Sulphur dissolves in hot & conc. solution of strong alkalis [NaOH,

KOH, Ca(OH)2] with formation of metallic sulphides &thiosulphates. The further

combine with excess of S yeilding poly sulphides.

4S + 6NaOH = 2Na2S + Na2S2O3 + 3H2O

Na2S + 4S = Na2S5.


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Oxygen Page 24


(2S + 3Ca(OH)2 = 2CaS5 + CaS2O3 + 3H2O

5. Metallic sulphites:- When a solm of Na or K sulphite is boiled with pawdered S,

thiosalpliate is produced

Na2SO3 + S 1000C Na2S2O3

(sodiumthiosulaphate)6. Action on oxidizing agent:- S ighites with emplosir when it is heated with oxidizing

agent like KClO3, KNO3

2KNO3 = 2KNO2 + 2O

S + 20 = SO2

7. With pol carbonate:- K2CO3 on being treated with excess of S, a mixture of

polysulphide&thiosulphate is obetaned. This brown aoloured substance is aalled liver of

sulphur.

6S + 2K2CO3 = 2K2S2 +K2S2O3 + 3CO3

Liver of sulphur

* Tests:- (i) sulphur is insoluble in water but soluble inCS2

(ii) S burns with a blue plame in air producing SO2 which is colourless & a pungent

smelling gas when this gas is passed through smelling gas. When this gas is passed

through acidified K2Or2O7solm, it turns green

K2Cr2O7 + 3SO2 + H2SO4 = K2SO4 + Cr2(SO4)3 + H2O

(orange) (green)

* Uses:- (i) Manufacture of SO2, H2SO4, CS2, S2Cl2, Na2S2O3

(ii) fungicides& disinfectant ultramarime

(iii) Colloidal sulphur & mil of S are used as medicines

(iv) Valcanisation of rubber

* At ord temp O2 is a colourless gas white S ia a pale yellow solid- Why ? O2 can formmultiple bonds & is diatomic, covalenty linked. The altractionbetnits individual

molecules is very weak & that is O2 is a gas. At ord temp, S aholecule consists of S atoms

which are cavalenty linked to form a puckered octahedral ring. As a result, its mol, wtincreases of so does the vanderurcle force

Properties O2 S8

Similarities

1. Pos in the p.t Same group 16, Valence

electrons 2 2 Group 16. Valence group

electrons 3 3


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Oxygen Page 25


2. Occurrence Occurs in free state Occurs in free state (less than

O2)

3. Allotropy O3 is the allotrope form S exists both in amorp hour &

crystalline form

4. catenation In In . 5. Hydrides & & 6. Action on metals Produces basic oxides which

prodices alkalis when

dissolved in

Porms metallic sulphides

prodike when dissolved in

acid

7. On non-metals Produces acidic oxides which

yeiled acids on treatrnent

with water

Produce sulphide, reacts with alkalis to produce

thiocarbonate 3 6 2 3 .

Dissimilarities

1. Physical state is a colourless gas at

ordinary temp

S is a pale yellow solid

2. Oxidation.No 2,2,1 2,4,63. Conbustibitity It is not combustible but

supports combustion

S is it selfcombusrible in air &

forms & 4. Action on NO Reaction Reacts with conc with

the formation of .5. Mol structure Diatomic & linear 8 atoms puckered ring6. Multiple bonds Due to small size O com form

multiple bonds

S due to its large size has very

feeble tendency I.e why

molecule is not

7. d-orbitals No vacant d-orbitals Enhibits tetra & well as

henavalency of d orbitals

Hydrogen Sulphide(

[A] PREPARATION:-

(i) 2 is prepared by the action of cold and dilute sulphuric acid on Fes.


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Oxygen Page 26


2 is collected by the upward displacement of air coz it is heavier than air, or aver hot

water as it is much less soluble in hot water

* Purification:- 2 wntains 2, Moisture & HCl gas (if 2 is prep by the action on HCl on

Fes)

The gas is passed through a sat. solm of sodium hydrogen sulphite to remove the HClvapours The gas is then passed there 2 5 which absorbs moisture. The gas is cooled by dry ice

when 2 becomes liquid. The uncondensed 2 is pumped out. This liquid 2 is

converted to gas at room temp

* or conc 2 4 is in the prep of 2 : Because of the fact that the2 produced by the action of an pes is oxidized to S due to the oxidizing action

of , and get it self its rednced to . So instead of 2 we get yellow ppt. of S

4 2 2 With conc 2 4, & 2

2 2 2 cannot be dried by or CaO or conc 2 4 but can be drive by 2 5 or

: Through fueed is a good drying agent, but it cannot be used to dry weak dibasic

acid, as it reacts with it to form cas& HCl

2 ii. Conc 2 4 being a strong oxidizing agent, oxidizes 2 to S due to the nascent Oproduced by its decomp

2 4 2 2 2 2 2

iii. is a basic oxide & 2 is a weak dibasic acid , reacts with to form&

2 5is a good brying agent as well as an acidic oxide. 2 being a weak acid does not

react with it being an amphoteric oxide also can be used

2. By heating an aquewussolm of thioaccetamide:-

3. By heating antimony sulphide with conc HCl:-


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Oxygen Page 27


6 2 3 (pure 2 )4. Porm metallic suplhides:- Metallic sulphides on bingtrcated with dil. HCl or 2

evolues 2 .

2 2 2 5. By the action of mascent 2 2 4 on non metallic sulphides:-

12 2 3 .6. Synthetic process by passing a mixture of 2& s vapours over mi cat at 4500C.

2 450

0 2

PROPERTIES:-

[A] PHYSICAL PROPERTIES:-

(i) 2 is a colourtes gas having an unpleasant amell resembling that of rotlen eggs.

ii. Pairlysouble in cold 2 but not in hot water

iii. It can heavier that air (v.d=17)

iv. It can easity be converted to a colourless liquid by cooling it to 60-70C or by

applying high pressure.

v. It is a poisonous gas &produces headache when inhated in small quantities

H2S is a gas but2

is liquid at room temp:- H- bond in2

molecules form a chain of

water molecules due to due the high eteronegatintiy & small size of O-atom. (cage like

structure with each 2 molecule linked to 4 2 molecules)

But due to the large size & small electrongativety of a stom, 2 cannot

form H- bond & the molecules are altracted only by weak vander waals force .


i. Combustibility:- 2 is a non-supporter of combustion but it burns in air or 2 with a

blue flame forming S d steam. In presence of excess of air it forms ,

2 2 , 2 3 2 2 An aq. Solm of 2 kept exposed in air becomes turbid cz the dissolved 2 ispartially oxidised by air to form insoluble S & as a result the solm. becomes turbid.

2 (air) = 2 Thermal decomposition:- when heated abobe 4000C 2 begind\s to decompose into

& . The decomp is comptated at 17000C


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Oxygen Page 28


2 2 3. Acid property:- The aq.som of 2 acts as a weak dibasic acid & is called hydro

sulphuric acid. It turns blue litmus red. Its aq. Som conducts electricity better than

water. It ionizes as follows:-

2 2 2It reacts with bases or alkalis to form salts with alkalis it gives 2 series of salts-acid salts(chloro sulphides) & normal salts (sulphides)

(sodium hydrogen sulphide)2 2 (sodium sulphide) 2

2 2 Metals which are above 2 in the e-series disp-lace 2 from 2 at elevated

temperature with the formation of the corresponding sulphides

,2 2 (black)

Hg, Ag which are below 2 in the e-series, yet the metals liberate 2 from 2 with the

formation on of the sulphides.

This is because & are highly stable compounds.

When 2 is made to react with these metals, the oxidation potentials of & Ag are

increased considerably making them very easly oxidisable to

&

. So thedisplacemert of 2 takes place.

, 2 4. Reducing Property:- 2 acts as a strong reducing agent as S in the -2 oxidation state

(lowest) for S compounder has an inherent tendency to inarease its oxidation no dt the

expense of reducing others.

2 2 2, 2 2

5. Formation of thionic acid:- At O0C, 2 reacts with an aq.som of with theformation of thionic acid

5 10 3 2 (penta thionic acid)

6. Sulphur is ppted when 2 is passed through an aq.som oif sodium disulphite

2 3 3


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Oxygen Page 29


7. Precipitation of sulphides:- 2 is used as mp reagent for the detection of basic

radicals in q.A.

Based on the solubilities of diff. metallic sulphides in diff. media, they are

classified as:-

i. Metallic sulphides which are insoluble in dil HCl:-Black CuS, PbS, HgS 4 2

2 4Yellow , , , . 2 & . . Orange , . [of these, AS, Sb, Sn are only]Brown , . soluble in yellow ammonimum

sulphide

ii. Metallic sulphides which are soluble in acid med but insoluble in alkaline

medium

white pptMnSbuff (pink) ppt

, , Black pptiii. Soluble in water:- The sulphides of alkali & alkaline earth metals are soluble in water

& are not ppted by water.

, , , etc + also of , , , * Separation of the metallic radicals from a mixture of salts:- Suppose a mixture contains

aq. Som of CuSO4, ZnSO4& Na2SO4. The mixture is dissolved indil HCl and H2S is passed

through the acidified som of the mixture, when CuS(black) being insoluble in del. HCl

gets ppted& is fittered off

The filtrate is the boiled to remove H2S and is made alkalime by adding

NH4OH. H2S is passed then this alk. Som when a white ppt. of ZnS is obtained. It is

separated by fitration& the filtrate contains No salt only. Thus they are separated

TESTS OF H2S:-

(i) H2S ahs a characteristic unpleasant smell that of rotten eggs.

(ii) It turns lead acetate paper black due to formantion of lead sulphide

3 2 2 2 3 (black)


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Oxygen Page 30


(iii) 2 does not change the colour of sodium nitroprueside, but when 2 is passed

through freshly prepared alkaline sodium nitroprusside solution, a violet colouration is

formed due to the formation of a complex salt.

2 2 (sodiumnitroprusside) (violet colour)

USES

(i) 2 is used in the prepn of polysulphides.

(ii) As a reagent for the detection of basic radicals in QA

* How would you obtain 2 from a metallic sulphate sulphate

heated

strongly by a blow pipe in the rednflame

(The sulpliate is first reduced by C particles)

4 4 2 2 2

* STRUCTURE:- In 2 the S atoms is surrowended by 2 lps and two H atoms. Like 2 ,

2 has a bent structure with H-S b-l = 1.35& H-S-H b.L = 92-50 which is much lessthan in 2 (104-50). This is attributed to the small electronegativity of S atom. Due to

the more electronegtivity of O, the b.p in 2 are nearer & repulsive interaction are

more while in H2 O, the b.p are awdy and hency repulsive interaction are less i.e whyHOH b.L is > HSH b.c

* H2S can be purified (inreqd) by passing it through HgO suspension in water

. (May hydrosulphide)* Allotropy of S:- 8 monoclinic sulphur (a third modification, apart from & Is nacreous (looks like mother of peral). It can be made by chilling not conc. soms of S in

solvents such as CS2 rings with a oroun conformation & differ only in the averallengelssulphur (e sulphur) is anstable and contains S6 rings arranged Na2S2O3 sol into conc

HCl &cetracting the S with totuene it can be made a sa follows:-

2 4 2 2 6 2 Several other ring S, Sq, S10, S11, S12, S18, S20 have also prepared by schxidt


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Oxygen Page 31


In all these ring coxpounds the S S dist is 2.04-2.06& the bondS S- S range from 1020 - 1080SULPHUR DIOXIDE

Preparation

By heating Cu turning with conc

2 4 . 2 4is reduced by metallic 2

is collected by the upward displacement of air.

* Lime cannot be used to dry , an acidic oxide 2cao(a basic oxide) reacts with producing calcium sulphite

By burning sulphur in air:- By the reduction of conc. 2 4:- may be abtained by the action of metals like Hg,

Ag & non metals like C, S on conc 2 4.

2

2 2 2 2 3 2

From sulphites and bisulphites:- At ord. temp , may be obtained by the action of dil.HCl or Dil 2 4 on sulphite and bisulhite salts. [non redon reaction]

2 2 2

2 2 Preparation of from sulphide ores:- During the extraction of metals like

, , , ,etc, is ottained as a hy-product when the sulphide ores of thesemetals are roasted. Thus is obtained by voasting zinc blend (zns) galena (pbs),

copper lysites 2 , 2 3, from pyrites( or fools gold)2 3 2 2 , 2 3 2 2 , 4 2 3

4 110 2 8 .By heating anhydrite 4, abt. From gypsam anhydrone MgClO

+

-1 -1


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Oxygen Page 32


With C above 10000C:-

2 2 2 PROPERTIES:-

[A] PHYSICAL PROPERTIES:-1. is a colourless gas having an irritating & suffocating smell of burning.

2. It is fairly soluble in waters.

3. It is nearly turce heavier then air.

4. It can be liquefied even at atm. Pressure at -100C. liquid SO2 is colourless liquid

(b.p = 100C) & used as non aqueoussowent It freezes at 72.70C to snow like mass

[B] CHEMICAL PROPERITES:-

1. Acidic properties:- is an acidic oxide. It dissolves in water to form 2 3 which is

dibasic & which blue litmess red. 2 3on being heated decomposes to give & .i.e., why is called anhydride of sulphurous acid.

[so is a more powerful reducing agent in alkaline medium than in acid medium]

, [Sulphites]When is passed through a som of at first their sulplites are formed. On

passing encess , the sulphites are converted to bisulphites

;

2.

With lime water, first forms insoluble CaSO3 due to which the clear solution turns

milky. On passing excess , xisulpate is formed & so the milkiness disappears. On

boiling the calcium disulphite som the milkiness reappears due to the decomp of

calcium disulphite into insoluble calcium sulphite & SO2

2 (milky) (milkiness disappears)

(reappears)* 2also gives similar test, but cannot reduce , 2. Combustibility:- is not combustible neither a supporter of combustion, but theburning Na, K, Mg, Fe, C etc continue to burn in the gas. Na or K burns in the gas to yield

sulphite&thiosulphate.

4 3 4 3


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Oxygen Page 33


Fe, Mg burn in SO2 with the formation of the their oxides & sulphides

3 2 , 3 2

In these reactions, SO2 is partly decomposed to give. If mascent oxygen due to high temp

by the burning metals.

3. Decomposition:- A sat. aqueoussom. Of SO2 on being heated in a sealed tube at 1500C,

s separates out from the som. As a yellow ppt. which dissolves in CS2.

2 2 2 33 2 all (Dispropor tionation)3 1000 2

4 2 3 4. Reducing property:- is a strong reducing agent in presence of moisture it canliberate moscent H or in presence of an oxidising agent it can easily take an oxygen

atom.

i. Through water:- 2 ii. Through water 2 2 iii. Through 2 in water:- 2 2 2 2 2 4iv.

2

2

v. 2 2 2 2 2. 2 2 7 clear green som.

In case of 2 (1) 4 dirty colourless som. Due to pption ofS. (2) 2 2 7 dirty green som. Is obtained.

The free S makes the som, turbid & gives a dirty appearance

2 2 7 3 2 4 2 4 2 4 2 43 3 7 2 2 5 3 2 89

viii. 2 2

2

2

3

2 4

ix. 2 7 5 4 3 2 x. 2 2 2 2 5. OXIDISING PROPERTY:- i. Burning Mg, Fe, K, Na etc continue to brown in

hite formation of sulphide & oxide (sulphites &thisulphates) in case of K, Na,

3 2 , 2

(colourles

(yello


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4 3 ,4 3 ii. when is passed over red hot ke at 11000C, C is oxidised to CO2

iii. 4 4 4 3 2 iv. 2 2 (This shos that H2S is stronger reducing agent thanSO2)6. FORMATION OF ADDITIVE COMPOUNDS:- forms additive compounds with

same elements or compounds. With Cl2 in presence to sunlight it forms sulphuryl

chloride.

Or camphor (sulphuryl chloride)

can form additive compounds but cannet:-

In the molecule of , has a Lp of electrons. These electrons can be donated tomonovalent atom like Cl to complete its octet. Thus to atoms of Cl accepts one electron

from the Lp of e of to form sulphuryl chloride.

But in , C atoms has no such Lp of electrons with whiath can form bonds with others

like

7. BLEACHING PROPERTY:- Perfectly dry has no bleaching property but in

presence of moisture it can bleach the vegetable colourless matters. It is due the fact

that in presence of moisture at, first with water producing 2 4 ith the evolution

of nascent hydrogen. This nascent H belaches the colouring matter to a colourless

compound by reduction.

2 2 Colouring matter

Reduced colourless reduction product.

The colourless (reduced) compound is reoxidised by air to coloured compound,

bleaching by is temporary.


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In certain cases, bleaching by takes place via the formation of colourless

sulphites &bisulphites.

The coloura can be restored by dipping the bleaching matter in dilute acids.

_ (colourless compound)

* Comparison of the bleaching props of SO2& Cl2:-

i. Both & require moisture for bleaching, cannot bleacu in the dry stateii. bleaches by redn through nascut H produced by reactionith 2 .

2 2 .Colouring matter

Colourless matter

in presence of moisture evolves nasceut O which bleaches the colouring matter tocolourless by oxidation.

2 Colouring matter

Oxidised colourless product.

iii. The bleaching action of is not permanet. The original of the fabrics may be

restored by sinply to aitr due to oxidising action of O2 of air. The bleaching action of ,

the substances cannot restore its original colour.

iv. is milder bleaching agent that & So delicate fabrics like silk, wool etc arebleachied by as these delicate farbics may be affeated by the action of .Sometimg action of may also harm the fibres.

TESTS

i. Colourless gas having smell of burning S.

ii. Changes colour of acidified soh of 2 2 7 from orange to green (clear),

from pink to colourless (clear) be redn. The same occurs ith 2 but a dirty som. Is

found due to turbidity of S.

iii. A picec of blotting paper, soaked in KIO3& starch som, is introduced in a jar of

. The paper turns blue as is reduced by to free 2.2 5 4 3 2

2


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Uses

1. As a bleaching agent

2. As an antichlor for removing sxcess from a fabric after

bleaching.3. In the paper of 2 4, sulphites & bisulphites4. In refining petroleum & sugar

5. As a refrigerating agent . 26. preservative& disinfectant for Killing geams, funge. (non

aqueous (SO2 ordinary)

7. Liq. is used as a solvent for many organic & inorganic

compounds.

Two 6 bonds These two form two & 1 Lp & bondsSP2hybridisationith oxygenIn molecule, each O atom is joined to sulphur by a 6 & a bond. The 6 bonds betn.

S & O are formed by SP2 P averlap& the other from overlap. The bond( is slighty reduced from 1200 to 119-50 CO2 of the presence of Lp on S.

It is imp to note that molecule has 2 diff. types of bonds & , but even then both the S O bonds are indentical (1 430A). this indicates that

is a ohezonace hybrid of the folloing 2 structures.

V shape of is in accordance ith its dipole moment (1 60D); had the molecule

been linear like its M would have been zero.

Due to presence of Lp of electrons in , it can act as leuris base.

Gascous SeO2 has the sanie structure but the solid form consists of infinite non-planar

shains of SeO2withbridging O-atoms

, is a gas & forms discrete molecules en in the solid state hile in the solidstate consisits of chains of units.

ACID RAIN


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A large amount of is released into the atmosphere from al & poer plants. It is also

accompanied by some oxides of N2, causing environmental pollution. These gases also

dissolve in rain water & make it acidic; acid rain hich is bad SO quantitative methods for

measuring in the atmosphere are highley devaueped like:-

1. Oxidation. To 2 4 hich is determined by titration 2. Reaction with 2 4 to give a Hg complex hich reacts with dyepararosaniline & is estimated calorinetrically.

2 4 2 2 2 2 2 32 4 3. Burning in a H flame in a inflame photometer& measuring the spectrum of S2

* is used to make other products:-

2 2

2

2

1.Colourless gas having a smell of burning s. 1. Colourless & odourless gas

2. Havier than air 2. heavier than air

3.fairly soluble in water, can be liquefied by

cooling.

3. fairly soluble in ater liquefied by applying

pressure at tem.

4. Neither combustible mor a supporter of

combustion but burning Na, K, Mg, Fe burn init

3Fe+SO2=2FeO+FeS.

4. Same as , strongly heate d metals like

Na, K, Mg etc continue to burn in it

2 2 .

5. Acidic oxide, forms 5. Acidic oxide 6. Alkalis forms sulphite&bisulphate

6. with alkalis forms carbonate & bicarbonate

salts. 2 2

7. + Ve lime ater test 7. + Ve lime water test

8. has reducing prop it can reduce acidified

, soms8. has no reducing property. does not

react with them

9. can act as an oxidies ng agent.

(yellow) Burning

9. only acts as oxidation agent . at high

temperature oxidiese metadllic zn to zno

but it cannot oxidize som


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&

10. has bleaching property. Bleaches

coloured matters by redn

10. No bleaching property.

11. Forms additive compounds like etc 11. Forms no additive compounds as the Catom in CO2 has no lone pair electrons

12. has V shaped molecule B.L = 119 50.

It has dipole moment = 1.60 D

12. is a linear molecule it has no dipole

moment

SULPHUR TRI-OXIDE (SO3)

anhydride of 2 4. 80PREPARATION

1. By the direct combination of & :-2

2. By the dehydration of conc. 2 4 is dehydrated by 2 5 to produce and

metaphoshoric acid

2 4 2 5 3 2 3 3. From metallic sulphates & bi-sulphates:-

3 2 2

PROPERITES:-

[A] PHYSICAL PROPERTIES:

i. SO3 is colourless transparent &erystalline solid

ii. itexixts in 3 forms:-


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(a) (m.p = 6220C):- It is obatanied as colourless needle sliaped transparent icelike crystals, when anhydrous vapour are cooled by liquid air when kept below

250C, it is converted to form.(b) (m.p = 32.50C):- on being exposed to moisture or kept belo 250C,change to silky white, soft absestos like needles. This is known as 3. its m w is 160 . It sublimaters at 500C at 50 1000C it change to .(c) (m.p = 160.80C at 2 atm pressure):- It is abtalned by completely drying the

varitely. It resembles icee-like structure (in appearance)& is a cyclik trimer

(SO3)3 is the most stable form & is made of chains cross linked into sheets.[B]CHEMICAL PROPERTIES:-

1. Decompostion:- decompess into & when passed through a red hot tube.

2

2 2. Action with ater:- has a strong offinites for water it reacts violenty withwater with a hissing sound producing sulphuric acid & pyro-sulphuric acid or olum.

, This racntaksplac with thvolution of much hat. Whn is kpt xposd to air, it combins

with th moistur to form whit fums of 2 4

, . is calld th anhydrid of 2 4.

3. Action with basic oxids:- is an acidic oxid it racts with many basic oxids & alkalis

to produc mtallic sulphats.

, ,2 .

4. Action with acids:- (a) combins with anhydrous HCl to form chloro sulponic

acid

. . (b) It is absorbd conc. 2 4 to produc olum or pyrosulphuric acid or fuming

2 4: 2 4 3 2 32 75. Oxidising proprty:- is a strong oxidising agnt sp. When hot.

(a) oxidises colourless to form red vapaurs of

2


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(b) 2 @ With urea:- reacts with urea acidified with 2 4 to make sulpharic acid

& . . 2 . .

Sulphuric acid is the only strong acid that exists as a solid at room temperature it is usedfor cleaning the plants at sugar refineries&traceries.

Group 16 elements

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Transcript of Group 16 elements