SAJC H2 CHEM Prelim Paper 2 Questions + Solutions

Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations CHEMISTRY Higher 2 9746/02 Paper 2 Structured 26 August 2008 1 hour 30 minutes Candidates answer in the space provided on the question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST 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 all questions 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. For examiner’s use Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Total This document consists of 21 printed pages including this page. - 3 -

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- 5 - 1. (a) Draw the dot-and-cross diagram of ClO4 - and predict the shape of the ion. [2] (b) In a particular titration reaction, sodium chlorate(VII ), NaClO 4, is titrated with an acidified aqueous solution of M3+ ions. Sodium chloride is formed in the process and the oxidation state of M changes from +3 to +4. If 12.50 cm3 of a 0.0500 mol dm -3 aqueous sodium chlorate requires 25.0 cm 3 of M3+ to reach the end point, what is the concentration of the M3+ solution? [3] [Total: 5 marks] [Turn over

- 6 - 2. (a) Using the following data, and relevant data from the Data Booklet, construct an energy level diagram to calculate the enthalpy change of solution of NaCl. Enthalpy change of formation of NaCl(s) -411 kJ mol-1 Enthalpy change of hydration of Na+(g) -390 kJ mol-1 Enthalpy change of hydration of Cl -(g) -381 kJ mol-1 Enthalpy change of atomisation of sodium +108 kJ mol-1 First electron affinity of chlorine -359 kJ mol-1 [5]

- 7 - 2. (b) Calculate the mass of water required to dissolve 11.70 g of NaCl if the temperature of the solution decreases from 25.0oC to 22.7oC. [Assume that the heat capacity of all solutions = 4.18 J cm-3 K-1] [2] [Total: 7 marks] [Turn over

- 8 - 3. Nitrogen can be recovered from nitrogen monoxide by reacting nitrogen monoxide with hydrogen gas at 700°C: 2NO(g) + 2H2(g) Æ N2(g) + 2H2O(g) A series of experiments was done to investigate the rate of the above reaction and the results are shown below. Experiment Initial concentration of NO (mol dm-3) Initial concentration of H2 (mol dm-3) Initial rate of reaction (mol dm-3 s-1) 1 0.050 0.001 0.025 2 0.050 0.003 0.075 3 0.100 0.006 0.600 (a) Deduce the order of the reaction with respect to (i) H2 (ii) NO [2]

3. (b) (i) The Boltzmann distribution curve for the reaction at 700°C is shown below. On the same diagram, sketch the Boltzmann distribution curve for the same reaction at 500°C (ii) By using the concept of collision theory, explain in general terms why temperature affects the rate of a chemical reaction. [3] [Total: 5 marks] [Turn over Fraction of molecules with energy E energy E activation energy - 9 -

- 10 - 2NH3(g) 4. Ammonia gas is produced industrially via Haber Process: A mixture containing 1.0 mol of N2(g) and 2.8 mol of H2(g) was allowed to reach equilibrium in a 2 dm3 closed reaction vessel. At equilibrium, it was found that 40% of N2(g) was converted to NH3(g) (a) Calculate the value of KC, giving its units. [4] N2(g) + 3H2(g)

4. (b) State and explain how the value of KC would change if 0.1 mol of ammonia gas is removed from the equilibrium mixture. [1] [Total: 5 marks] [Turn over - 11 -

- 12 - 5. An unknown volume of a weak monobasic acid, HA, was titrated against 0.200 mol dm-3 aqueous sodium hydroxide and the following curve was obtained. Using the graph, (a) determine the acid dissociation constant, K a, of HA. [2] (b) determine the concentration of HA. [2]