(a)(i) State three methods of preparing salts, giving one example in each case of a salt so prepared. (ii) What type of salt is each of the following? NaHPO; (CHCOO)Pb; KAI(SO). 12HO.
(b)(i) Write an equation for the reaction between dilute HCI and a solution of AgNO. (ii) Explain why NaNO is preferred to AgNO in the preparation of oxygen by thermal decomposition of trioxonitrate (V) salts. (iii) When silver wire was dipped into an aqueous solution of CuSO, the wire remained intact but when the wire was replaced with zinc rod, the rod decreased in size. Give an explanation for this observation.
(c) When a sample of a crystalline salt X was exposed to air, there was a loss in mass. (i) What phenomenon was exhibited by X? (ii) Suggest two substances which X could be. (iii) On heating 5.00 g of a fresh sample of X to constant mass, 1.80g was lost in the form of water vapour. Calculate the number of molecules of water of crystallization in one molecule of X. [H = 1.00; O = 16.00; Anhydrous form of X = 160 g mol
Explanation
(a)(i) - By the action of a dilute acid on a metal e.g. Zn + 2HCI --> ZnCl + H or Mg + HSO MgSO + H - By neutralisation of an alkali by an acid e.g NaOH + HCI -> NaCI + HO -By the action of a dilute acid on an insoluble base e.g 2HCI + MgO -> MgCl + HO -By the action of a dilute acid on a trioxocarbonate (IV) e.g 2HCI + CaCO CaCl ± H O + CO (ii) NaHPO -An acid salt; (CHCOO) Pb -An organic salt KAI(SO) . 12HO - hydrated double salt
(b)(i) HCI + Ag NO -> AgCI + HNOO (ii) NaNO is preferred to AgNO in the thermal decomposition to give O because NaNO decomposes to only solid and O gas making it easy to collect, unlike AgNO which decomposes into silver, oxygen and nitrogen (IV) oxide. (iii) Silver cannot displace Cu in the solution of CuSOCO. 10HO or CuSO .10HO. -mHO (iii) X .mHO X. from the heat equation 160 + 18m --> 160 ; 5 ->1.80 heat = 288 + 32.4m = 512 m = = 15.8 m = 16 molecules
