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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

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Group - 14 Elements - The Carbon Family

Group - 14 Elements - The Carbon Family
The group 14 (IVA) elements - carbon, silicon, germanium, tin and lead are especially important both in industry and in living organisms.


GROUP - 14 ELEMENTS - THE CARBON FAMILY

The group 14 (IVA) elements - carbon, silicon, germanium, tin and lead are especially important both in industry and in living organisms.

1.           Carbon is an essential constituent of the molecules on which life is based.

2.           Silicon is the second most abundant element in the earth's crust.

3.           Bothsilicon and germaniumare used in making modern solid-state electronic devices.

4.     Tin and lead have been known and used since ancient times.

 

General Trends

Electronic configuration: The elements of this group possess ns2 np2 electronic configuration.

 

Electronic Configuration of Group 14 elements

Carbon -

Atomic Number :  6   Electronic Configuration :  [He] 2s2 2p2     Group Number  : 14  Period Number : 2 

Silicon -

Atomic Number :   14  Electronic Configuration :  [Ne] 3s2 3p2     Group Number  : 14  Period Number : 3 

Germanium -

Atomic Number :   32  Electronic Configuration :  [Ar] 3d10 4s2 4p2    Group Number  : 14  Period Number : 4 

Tin -

Atomic Number : 50  Electronic Configuration :   [Kr] 4d10 5s2 5p2   Group Number  : 14  Period Number :  5

Lead -

Atomic Number :  82   Electronic Configuration :    [Xe] 4f14 5d10 6s2 6p2  Group Number  : 14  Period Number : 6 

 

1 Silicones - structure and uses

The silicones are a group of organosilicon polymers. They have a wide variety of commercial uses.

The complete hydrolysis of SiCl4 yields silica SiO2, which has a very stable three-dimensional structure. The fundamental research of F.S. Kipping on the hydrolysis of alkyl-substituted chlorosilanes led, not to the expected silicon compound analogous to a ketone, but to long-chain polymers called silicones.


The starting materials for the manufacture of silicones are alkyl-substituted chlorosilanes. Thus the hydrolysis of trialkylmonochlorosilane R3SiCl yields hexa- alkylsiloxane.


The dialkyldichlorosilane R2SiCl2 on hydrolysis gives rise to straight chain polymers and, since an active OH group is left at each end of the chain, polymerisation continues and the chain increases in length.


The hydrolysis of alkyl tricholorosilane RSiCl3 gives a very complex cross- linked polymer.


Uses

1.           Silicones act as excellent insulators for electric motors and other appliances as they can withstand high temperatures.

2.           Straight chain polymers of 20 to 500 units are used as silicone fluids. They are water repellent because of the organic side group. These polymers are used in waterproofing textiles, as lubricants and as polish.

3.           Silicone rubber retain their elasticity even at low temperatures and resist chemical attack. They are mixed with paints to make them damp-resistant.

4.           Silicone resins, a cross-linked polymer used as non-stick coating for pans and are used in paints and varnish.

5.           Silicone oils are highly stable and non-volatile even on heating. Hence used for high temperature oil bath, high vacuum pump etc.

 

 

2 Metallurgy of Lead

 

Ores

1.      Galena    PbS

2.     Cerrusite PbCO3

3.     Anglesite PbSO4

4.     Lead ochre PbO

Extraction: Lead is mainly extracted from the sulphide ore galena. Galena

contains lead sulphide and small quantities of silver.

1.    Concentration: The ore is concentrated by froth floatation process.

2. Smelting in a Reverberatory furnace: The concentrated ore is roasted in a reverberatory furnace at a moderate temperature. The temperature of furnace is controlled by regulating the air supply. During roasting, galena is partly oxidized to lead monoxide and partly to lead sulphate.

2PbS + 3O2        2 PbO + 2SO2

PbS + 2O2            PbSO4


More of galena is then added. The temperature is raised and simultaneously the air supply is reduced. Lead sulphide reacts with the two oxidised products giving lead.


PbS+2PbO 3Pb+SO2

PbS+PbSO4   2Pb+2SO2

Thus in this process roasting and smelting are carried out in the same furnace,

at two different temperatures.

About 90% of lead is obtained as metal, the rest passes into slag. Lead is

recovered from the slag by heating with lime and powdered coke.


Purification of Lead

Lead extracted by the above method contains impurities such as silver, copper, tin, bismuth, gold and iron. It is refined by the following processes.

a. Liquation

The impure metal is heated on a sloping hearth. Lead melts and flows down the slope. The infusible impurities remain on the hearth.

b. Desilverisation

Silver is removed by either Pattinson's process or Park's process.

c. Electrolytic refining

Very pure lead is obtained by this process.

Anode - Impure lead

Cathode - Very pure lead

Electrolyte - Lead fluosilicate + Hydrofluosilicic Acid

(PbSiF6)      (H2SiF6)

 

The metallic impurities which are more electropositive than lead, such as iron and tin, go into the solution while the rest of the impurities are thrown down as anode mud.

 

Physical properties

 

1.           Lead is a bluish grey metal with a bright luster.

2.           It is soft and can be cut with a knife and drawn into a wire and rolled into a sheet.

3.           It is not a good conductor of heat and electricity. It marks paper.

Chemical properties

1. Action of air

       i.            It is unaffected by dry air but in moist air a layer of lead carbonate or lead hydroxide is deposited on its surface which protects it from further action of air.

     ii.            When heated in air or oxygen, lead is oxidized to litharge (PbO) and red

lead (Pb3O4)

2Pb + O2  2PbO 3Pb + 2O2  Pb3O4

2. Action of water

Lead is not attacked by pure water in the absence of air, but water containing dissolved air has a solvent action on it due to the formation of lead hydroxide (a poisonous substance). This phenomenon is called Plumbo solvency.

2Pb + O2 + 2H2O               2Pb(OH)2

3.    Action of acids

i) Dilute H2SO4 and HCl have no action on lead.

ii) Hot Conc. H2SO4 liberates SO2 but the reaction is retarded by the formation

of an insoluble layer of lead sulphate.

 

Pb + 2H2SO4 PbSO4 + 2H2O + SO2

iii) Concentrated HCl evolves hydrogen and also forms Chloroplumbic acid

Pb + 2HCl          PbCl2 +H2

PbCl2 + 2HCl --- > < ---     H2PbCl4 (chloroplumbic acid)

 

Uses: Lead is used

       i.            For making lead pipes,

     ii.            For making telegraph and telephone wires,

  iii.            In making bullets and lead accumulators,

  iv.            In lead chambers, for the manufacture of sulphuric acid,

     v.            For making alloys like solder, pewter and type metal,

       vi.                        For preparing tetraethyl lead (Pb(C2H5)4) which is used as an additive to petrol to prevent knocking

 

Problem

An element A belongs to 14th group and occupies period number 6. A

reacts with conc. HCl. to give B an acid. A is used to prepare C which is used as an antiknock in automobiles. Identify the element A and the compounds B and C Write the reactions.

Solution

1.    As per the position in the periodic table, the element A is lead. 2. Lead with Conc. HCl gives B

Pb + 4 HCl H2PbCl4 + H2

Compound B is chloroplumbic acid.

3.   Compound C is tetraethyl lead.

 

 

 

 

 

 

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