NYJC H2 Chem 2013 Prelim P2 QP

H2 Chemistry 9647/02 NYJC J2/2013 Prelim [Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9647/02 Paper 2 Structured Questions 23 September 2013 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet. READ THESE INSTRUCTIONS FIRST Write your name and class 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 all questions in the spaces provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /22 3 /10 4 /18 5 /10 Total /72 This document consists of 17 printed pages. 23

2 H2 Chemistry 9647/02 NYJC J2/2013 Prelim For Examiner's Use Answer all questions in the spaces provided. 1 Planning (P) Acids can be classified in terms of t heir basicity depending on the number of protons that can be donated to a base. A st udent is investigating the basicity of a solution of 0.80 mol dm-3 acid, A, using just the acid and sodium hydroxide of the same concentration. He conducted two ex periments by mixing different volumes of A and sodium hydroxide, and taking the temperature rise for each experiment. (a) Based on the definition of the enthalpy change of neutralisation (∆Hn) and his results, deduce the basicity of acid A. Experiment Volume of acid Volume of NaOH ∆T /oC 1 40 20 3.6 2 20 40 7.2 ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [2] (b) (i) The temperature rise of the reaction can be det ermined graphically by measuring how the temperature changes with time. You are to plan an experiment to determine the ∆H n between a solid sample of A and sodium hydroxide. You are provided with a solid sample of A (M r = 174) and sodium hydroxide solution of 0.80 mol dm-3. In your plan, you should give:  details including calculations to determine the quantities of the reactants to be used;  choice of apparatus (You may use appar atus normally found in the school laboratory.);  the essential details for obtaining t he graph of temperature against time in order to determine the temperature rise;  table(s) of readings to taken. 24

3 H2 Chemistry 9647/02 NYJC J2/2013 Prelim [Turn Over For Examiner's Use Calculations: Procedure: …………….…………………………………………………………….………………… ……………….………………………………………………………….………………… ………………….……………………………………………………….………………… …………………….…………………………………………………….………………… ……………………….………………………………………………….………………… ………………………….……………………………………………….………………… …………………………….…………………………………………….………………… ……………………………….………………………………………….………………… ………………………………….……………………………………….………………… …………………………………….…………………………………….………………… …………………………………….…………………………………….………………… Table of Results 25

4 H2 Chemistry 9647/02 NYJC J2/2013 Prelim For Examiner's Use (ii) Sketch the graph that you would ex pect, showing clearly how you can determine the temperature rise. [8] (c) Explain why temperature rise in the experiment should not be too low. …………………………………………………………………………………………….… ………………………………………………………………………………………………. [ 1 ] (d) An alternative method to determine the temp erature rise is to measure the highest temperature reached. Explain if this is a better method. …………………………………………………………………………………………….… ………………………………………………………………………………………………. [1] [Total: 12] 26

5 H2 Chemistry 9647/02 NYJC J2/2013 Prelim [Turn Over For Examiner's Use 2 One of the most impo rtant features of the transition elements is that they exhibit variable oxidation states. This question illustrates the various oxidation states shown by iron in its compounds. (a) The reaction between iodide ions, I -, and peroxidisulfate ions, S2O8 2-, is slow. The reaction can be catalysed by adding a small amount of Fe2+ ions. The initial rate of the slow reaction bet ween iodide ions and peroxidisulfate ions can be studied by using thiosulfate ions. The equations for the reactions are as follows. 2I - + S2O8 2- I2 + 2SO4 2- (slow) reaction I I 2 + 2S2O3 2- 2I- + S4O6 2- (fast) reaction II In the presence of a cons tant amount of th iosulfate ions, the iodine being slowly produced by reaction l will immediately react in reaction ll until all the thiosulfate ions has been used up. At t hat point, free iodine will be present in the solution, which will cause a sudden appearance of a deep blue colour if starch is present. A series of experiments was carried out using different volumes of the five reagents. The following results were obtained. Expt Volume of S 2O8 2- /cm3 Volume of I- /cm3 Volume of S2O3 2- /cm3 Volume of distilled water /cm3 Volume of Starch /cm3 Time for the appearance of deep blue colour/s 1 20 20 10 5 5 30 2 20 15 10 10 5 40 3 5 25 10 15 5 t 3 4 10 15 10 20 5 80 (i) If the orders of reaction with respect to peroxidisulfate ions and iodide ions are both one respectively, deduce an ex pression relating the volume of these two reactants and time taken for the appearance of deep blue colour. Explain your reasoning. 27

6 H2 Chemistry 9647/02 NYJC J2/2013 Prelim For Examiner's Use (ii) Hence, predict the time, t3, required for the appearance of deep blue colour in experiment 3. ……………….………………………………………………………………………… …………………….…………………………………………………………………… ………………………….……………………………………………………………… ……………………………….………………………………………………………… [3] (b) (i) In the Haber process, the rate of formation of ammonia is increased by using an iron catalyst. State the type of catalysis occurring here and describe using the Maxwell-Boltzmann Distribution curve, how the iron catalyst increases the rate of reaction. …………………….…………………………………………………………………… ………………………….……………………………………………………………… …………………….…………………………………………………………………… ………………………….……………………………………………………………… (ii) Ammonia shows significant deviations from the ideal behaviour that is predicted by the kinetic t heory of gases. State two assumptions of the kinetic theory of gases. ……………….………………………………………………………………………… …………………….…………………………………………………………………… ………………………….……………………………………………………………… …………………….…………………………………………………………………… 28

7 H2 Chemistry 9647/02 NYJC J2/2013 Prelim [Turn Over For Examiner's Use (iii) A sample of ammonia can be liquefied at room temperature just by increasing the pressure of the sample. Why does the application of pressure cause the gas to liquefy? …………………….…………………………………………………………………… ………………………….……………………………………………………………… …………………….…………………………………………………………………… ………………………….……………………………………………………………… [7] (c) Iron(III) chloride is a dark brown solid which dissolves in water to give an acidic solution. This solution is often used, in the electronics industry, to etch (dissolve) the copper used in printed circuit boards. (i) Explain, with the aid of a chemical equation, why aqueous iron(III) chloride is acidic. …………………….…………………………………………………………………… ………………………….……………………………………………………………… …………………….…………………………………………………………………… (ii)