Set 19 Chemistry [Paper] 2

1 SECTION A (60 Marks) Answer only three questions from this section . 1. (a) When 6.1g of an organic compound P was completel y burnt in oxygen gas, yielded 15.4 g of carbon dioxide and 2.7g of water were formed . When 0.252 g of P was vaporized at 273ᵒc and 2.15atmospheres , it occupied a volume of 43.04c m3. i) Calculate empirical formula of P. (02½ marks) ii) Determine the molecular formula of P. (02½ marks) b) P burns with a sooty flame. Identify P. (0½ mark) c) When P was treated with lithium tetrahydridoaluminate (III) in dry ether, Compound Q was formed. When Q was warmed with acidified solution of chromium trioxide, Compound R was formed. i) Identify Q and R. (01 mark) ii) Write equations l eading to the formation of Q and R. (02 marks) d) Write equation and suggest a mechanism for the reaction between: i) Q and propanoylbromide. (03 ½ marks) ii) R and 2, 4-dinitrophenylhydrazine in acidic medium. (04½ marks) e) Without using equations , describe how P can be synthesized from benzene. (02½ marks) 2. Phosphorus (V) chloride decomposes at high temperature according to the following equation below. PCl5(g) PCl3(g) + Cl2(g) a) Write an expression for the equilibrium constant , KC for the reaction. (01 mark) b) The bond energies of P -Cl and Cl - Cl bonds are -276.6 and -242KJ/mol respectively. Calculate the enthalpy change for the decomposition reaction . (03 marks) c) State and explain the effect on the equilibrium position and value of the equilibrium constant for the equilibrium when: i) Pressure was increased. (03 marks) ii) Temperature was increased. (03 marks) iii) Inert gas was added at constant volume. (02 marks) d) When 83.4g of phosphorus (V) chloride was sealed in a 9.23dm3 glass tube …