JJC H2 Chem 2013 Prelim P3 QP

[Turn over JURONG JUNIOR COLLEGE 2013 JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 17 September 2013 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This document consists of 11 printed pages and 1 blank page. 619

2 © Jurong Junior College 9647/03/PRELIM/2013 Answer any four questions. 1 Nitric acid, HNO 3, is a common laboratory reagent and an important industrial chemical for the manufacture of fertilisers and explosives. (a) Nitric acid can be used to prepare lead( II) nitrate, Pb(NO 3)2, which does not occur naturally. When lead is dissolved in aqueous nitric acid, a brown gas is evolved during the reaction. (i) Use the Data Booklet to construct an equation for the reaction of aqueous nitric acid with lead. A 40 cm 3 s a m p l e o f P b ( N O3)2(aq) was prepared and then mixed with 60 cm3 of 0.100 mol dm3 Al2(SO4)3(aq), which is in excess. Upon mixing, a precipitate is formed which is removed. The final solution X that remained is found to be weakly acidic. (ii) With the aid of an equation, explain why solution X is acidic. (iii) Given that the acid dissociation constant, K a, of solution X is 1.4  105 mol dm3, calculate [H+] in solution X. [5] (b) During the industrial manufacture of nitric acid, NO 2 is hydrolysed by passing the gas through water. 3NO2(g) + H2O(l)  2HNO3(aq) + NO(g) Hr The following enthalpy changes are given: H /kJ mol1 N2(g) + O2(g)  2NO(g) +183 2NO(g) + O2(g)  2NO2(g) 116 2N2(g) + 5O2(g) + 2H2O(l)  4HNO3(aq) 256 (i) Using relevant data from the table above, calculate the enthalpy change of formation of NO 2(g). (ii) Using your answer in (b)(i) and any relevant data in the table, calculate Hr, the enthalpy change of reaction for the hydrolysis reaction of NO2. [3] (c) When concentrated nitric acid is reacted with concentrated sulfuric acid, the nitronium ion, NO 2 +, is produced, according to the following equation. HNO3 + H2SO4  NO2 + + HSO4  + H2O (i) Draw a dot-and-cross diagram of the HNO3 molecule. (ii) Hence, suggest why HNO3 acts as a Bronsted base in this reaction. [2]