Lead is an excellent roofing material. It is malleable and resistant to corrosion. Lead rapidly becomes coated with basic lead carbonate which protects it from further corrosion.
(a) Lead has a typical metallic structure which is a lattice of lead ions surrounded by a ‘sea’ of mobile electrons. This structure is held together by attractive forces called a metallic bond.
(i) Explain why there are attractive forces in a metallic structure.
(ii) Explain why a metal, such as lead, is malleable.
(b) Basic lead(II) carbonate is heated in the apparatus shown below. Water and carbon dioxide are produced.
(i) Silica gel absorbs water. Silica gel often contains anhydrous cobalt(II) chloride. When this absorbs water it changes from blue to pink.
Suggest a reason.
(ii) Soda lime is a mixture of sodium hydroxide and calcium oxide. Why do these two substances react with carbon dioxide?
(iii) Name two substances formed when soda lime reacts with carbon dioxide.
(c) Basic lead(II) carbonate has a formula of the type xPbCO3.yPb(OH)2 where x and y are whole numbers.
Determine x and y from the following information.
PbCO3 → PbO + CO2
Pb(OH)2 → PbO + H2O
When heated, the basic lead(II) carbonate gave 2.112 g of carbon dioxide and 0.432 g of water.
Mass of one mole of CO2 = 44g
Mass of one mole of H2O = 18g
Number of moles of CO2 formed = ………. .
Number of moles of H2O formed = ………. .
Formula of basic lead(II) carbonate is ___
(a)
(i) The attractive forces in metallic bonding arise from the electrostatic attraction between the positively charged metal ions (Pb2+) and the ‘sea’ of delocalized electrons.
(ii) Lead is malleable because its layers of metal ions can slide over each other without breaking the metallic bonds (non-directional bonding).
(b)
(i) The color change (blue → pink) occurs because anhydrous CoCl2 forms hydrated cobalt chloride (CoCl2·6H2O).
(ii) Soda lime reacts with CO2 because:
– CO2 is acidic (forms carbonic acid in water).
– NaOH and CaO are bases (neutralize acids).
(iii) Products: sodium carbonate (Na2CO3) and calcium carbonate (CaCO3).
(c)
– Moles of CO2 = 2.112 g ÷ 44 g/mol = 0.048 mol (from PbCO3).
– Moles of H2O = 0.432 g ÷ 18 g/mol = 0.024 mol (from Pb(OH)2).
– Ratio of PbCO3:Pb(OH)2 = 0.048:0.024 = 2:1.
– Formula: 2PbCO3·Pb(OH)2.
