d Block Elements : Tin and Lead

 

Tin and Lead 

Tin

Ores of Tin : Cassiterite or tin stone (SnO2)

  • The concentrated and roasted ore is reduced with carbon to get impure tin which is purified by liquation process.
  • Tin forms two series of salts, i.e., Sn (II) and Sn (IV). Whereas Sn (II) salts are ionic Sn (IV) salts are covalent.
  • Tin dissolves in hot conc. NaOH forming Na2SnO3 and evolving H2
  • Tin reacts with conc. HNO3 forming metastannic acid (H2SnO3).
  • Tin is not attacked by organic acids and hence is used for tinning of utensils to resist corrosion. Tin foils are used for wrapping cigarettes, confectionary items and for making tooth-paste tubes.
  • SnO2 is an amphoteric oxide.
  • Stannous chloride (SnCl2) acts as a good reducing agent. It reduces HgCl2 to first Hg2Cl2 and then to Hg. It also reduces FeCl3 toFeCl2
  • Stannic chloride (SnCl4) is a liquid and fumes in air due to hydrolysis. It acts as a Lewis acid and dissolves in concentration HCl forming H2SnCl6.
  • SnCl4. 5H2O is called butter of tin.
  • SnS dissolves in yellow ammonium sulphide.

 

Lead

Ores of lead : Galena (PbS), Anglesite (PbSO4) and Cerussits (PbCO3).

  • Lead is extracted from galena. The ore is concentrated by froth-floatation process and roasted when a part of the ore is converted into PbO and PbSO4. The unchanged galena then brings about the reduction of PbO or PbSO4 to Pb.
  • Lead dissolves in hot conc. NaOH forming sodium plumbite (Na2PbO2) and evolving H2 gas.
  • Leads forms two series of salts, i.e., Pb (II) and Pb (IV) but Pb (II) compounds are more stable than Pb (IV) compounds. Lead (II) compounds are essentially ionic while lead (IV) compounds are covalent.
  • Lead is used in making bullet shots, lead accumulators, tetraethyl lead (antiknocking agent) and a number of pigments such as red lead (Pb3O4), white lead or basic lead carbonate [2PbCO3. Pb(OH)2] and lead chromate (PbCrO4).
  • Litharge is PbO. It is obtained by heating Pb(NO3)2 or PbCO3. It is an amphoteric oxide and is reduced back to Pb by H2, C and CO.
  • Red lead (Pb3O4) or Sindhur is a mixed oxide (2PbO.PbO2). It acts as an oxidising agent and as such oxidises HCl to Cl2.
  • Lead dioxide (PbO2) is obtained either by treating Pb3O4 with conc. HNO3 or by treating lead acetate with bleaching powder. It acts as an oxidising agent and oxidises HCl to Cl.
  • The ionic character of lead dihalides decreases the order

PbF2 > PbCl2 > PbBr2 > PbI2.

  • PbF4 and PbCl4 are stable while PbBr4 and PbI4 are however, unknown. The non-existence of PbBr4 and PBI4 is due to strong oxidising character of Pb4+ ions and reducing character of Brand ions.
  • PbF4 is ionic while PbCl4 is a volatile liquid.
  • Lead is readily corroded by water containing dissolved air forming Pb(OH)2 which has appreciable solubility in water. This action of water on lead called is Plumbosolvency.

2Pb + 2H2O + O2 → 2Pb(OH)2

Whereas organic acids, NH4+ salts and nitrates increase while salts like carbonates, phosphate and sulphates decrease a. Hard water, however, has no solvent action on lead.

 

d Block Elements : Gold and its Compounds