1. (a) If 112 cm3 of hydrogen sulphide is mixed with 120 cm3 of chlorine at STP what mass of sulphur is formed? H2S + Cl2 —> 2HCl + S   2. (b) Washing soda has the formula Na2CO3. 10H2O. What mass of anhydrous sodium carbonate is left when all the water of crystallization is expelled by heating 57.2 g of washing soda?   3. (c) When excess lead nitrate solution was added to a solution of sodium sulphate, 15.15 g of lead sulphate were precipitated. What mass of sodium sulphate was present in the original solution? Na2SO4 + Pb(NO3)2——> PbSO4+ 2NaNO3 (H = 1; C = 12; O = 16; Na = 23; S = 32; Pb = 207)