NJC H2 Chem 2012 Prelim P3 QP

CANDIDATE NAME SUBJECT CLASS NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 REGISTRATION NUMBER CHEMISTRY 9647/03 Paper 3 Free response Tues 18 Sep 2012 2 hours READ THESE INSTRUCTIONS FIRST Answer any four questions. Start your answer to each question on a fresh piece of paper. 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 behind the cover page. This paper consists of 13 printed pages including 1 blank page.

NJC/H2 Chem/03/2012 [Turn over 2 Answer any four questions. 1 (a) The graph below shows the variation of pV versus p for NH 3, which exists as a gas under normal room conditions. Explain the shape of the graph, commenting on the behaviour of NH 3 gas as an ideal gas at A, B, C and D. [3] (b) Ammonia is manufactured by the Haber Process, using gaseous nitrogen and hydrogen. 3H 2(g) + N2(g) 2NH3(g) DH = –92.4 kJ mol–1 In an experiment starting with a 3:1 ratio of H 2 and N2 mixture at 400 oC and a constant total pressure of 200 atm in the presence of iron catalyst, the equilibrium mixture was found to contain 36.3 % by volume of ammonia. (i) Justify the conditions of temperature and pressure used. (ii) Write an expression for K p of this reaction. (iii) Calculate the partial pressures of each of these three gases at equilibrium, and hence calculate K p at this temperature, stating its units. [6] (c) Hydrazine, NH 2NH2 , is a flammable liquid with ammonia-like odour. It has basic chemical properties like ammonia. Compound NH2NH2 NH3 Kb / mol dm–3 1.3 x 10–6 1.8 x 10–5 Explain the difference in the K b values of these two compounds. [2] A B C D Ideal gas NH3 pV / J p / atm

NJC/H2 Chem/03/2012 [Turn over 3 1 (d) Hydrazine is miscible with water but immiscible with trichloromethane. (i) Explain, in terms of bonding, and with appropriate diagrams to illustrate, the difference in the miscibilities of hydrazine with the two stated solvents. (ii) Hydrazine hydrate, made from hydrazine, takes part in the following reaction: NH2NH2.H2O + IO3– + 2H+ + Cl– ® N2 + ICl + 4H2O Calculate the change in the oxidation states of the species oxidised. [4] (e) Hydrazines are part of many organic syntheses and undergo condensation reactions with carbonyl compounds. Below is a scheme showing some reactions of phenylethanone, which includes the reaction mentioned. COCH3 H2 /Ni T, P Compound B Reagent X NH2NH2 Compound A Compound C phenyle