TJC H2 Chem 2013 Prelim P1 QP & Soln

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2   9647/01/TJC Prelim 2013 [Turn Over  Section A For each question there are four possible answers, A, B, C and D. Choose the one you consider to be correct. 1 In which pair do both atoms have the same number of unpaired electron in their ground states? A Ca, Ni B Na, Sc C N, Fe D Fe, Cr 2 Silicon, phosphorus and sulfur are in Period 3. Which of the following statements best explains why silicon   (1s 2 2s 2 2p 6 3s2 3p2) has a lower first ionisation energy than phosphorus (1s2 2s2 2p6 3s2 3p3)? A Silicon has fewer electrons than phosphorus. B The 3p electrons of phosphorus do not experience inter-electronic repulsion. C The 3p electrons of phosphorus are further away from the nucleus. D Phosphorus has more protons than silicon. 3 Comproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, form a product in which the element involved reaches the same oxidation number in the product. 1 mol of potassium iodide undergoes comproportionation with compound X to form 0.6 mol of iodine. What could be the identity of compound X? A KIO2 B IO2 C KIO3 D KIO4 4 A pure hydrocarbon was completely isolated from a fractional distillation column in a refinery. When 10 cm3 of the hydrocarbon was burned in excess oxygen, the volume of the mixture decreased by 30 cm 3. On passing the resultant mixture through a solution of sodium hydroxide, the volume further decreased by 30 cm 3. All volumes were measured at room temperature and pressure. What is the formula of the hydrocarbon? A C2H6 B C3H6 C C3H8 D C4H10 1312

3   9647/01/TJC Prelim 2013 [Turn Over  5 2,4-dinitrophenylhydrazine (Brady’s reagent) is a common reagent used to qualitatively test for carbonyl groups associated with aldehydes and ketones. What would you expect the bond angles, x, y, and z to be, to the nearest 1 degrees, in the molecule of 2,4-dinitrophenylhydrazine? x y z A 107 120 120 B 107 107 109 C 109 120 120 D 120 107 120 6 Given the enthalpy change of the following reactions Fe 2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g) H = –26.8 kJ FeO(s) + CO(g)  Fe(s) + CO2(g) H = –16.5 kJ Find the enthalpy change for the reaction below Fe2O3(s) + CO(g)  2FeO(s) + CO2(g) A –59.8 kJ B –43.3 kJ C –10.3 kJ D +6.2 kJ 7 For a chemical reaction, A  B ∆H = +67.0 kJ mol–1 ∆S = –131 J K–1 mol–1 Which of the following statement is correct? A The reaction will be spontaneous when temperature is less than –511 K. B The reaction will be spontaneous when temperature is greater than –511 K. C The reaction will be spontaneous at any temperature. D The reaction will not be spontaneous at any temperature. 1313

4   9647/01/TJC Prelim 2013 [Turn Over  8 Use of the Data Booklet is relevant to this question. The following values for the cell potential were determined as a change was continuously made. reading number cell potential / V 1 0.770 2 0.980 3 1.064 4 1.093 ….… ….… 20 1.330 What continuous change in the Fe3+/Fe2+ half-cell could produce these results? A Increasing the concentration of Fe2+ (aq) in the Fe3+/Fe2+ half-cell. B Replacing the Pt electrode with a Fe electrode. C Adding acidified potassium dichromate(VI) into the Fe3+/Fe2+ half-cell. D Increasing the concentration of H+ (aq) in the H+/H2 half-cell. 9 Molten solutions of AgNO3, Cu(NO3)2 and Cr(NO3)3 are arranged in series and is subjected to a current of 2.0 A for 20 minutes. What is the relative amount of each metal formed? A Ag > Cu > Cr B Ag = Cu = Cr C Ag < Cu < Cr D Cu > Ag > Cr Pt electrode 1314

5   9647/01/TJC Prelim 2013 [Turn Over  10 Chromium plating is applied by electrolysis to objects suspended in an acidified dichromate (VI) solution. How long (in minutes) would it take to apply a chromium plating 0.2 mm thick to a car bumper with a surface area of 0.30 cm 2 in an electrolytic cell carrying a current of 10.0 A? (The density of chromium is 7.19 g/cm3) A 0.800 minutes B 2.70 minutes C 8.10 minutes D 48.0 minutes 11 Ammonia decomposes into hydrogen and nitrogen gas at high temperatures. 2NH3(g) N2(g) + 3H2 (g) Ammonia at pressure P was placed in an evacuated reactor which was maintained at constant temperature. At equilibrium, the ratio of nitrogen to ammonia was found to be 1:3. What is the equilibrium constant, Kp, for the reaction? A 3P2 B 75P2 C 3 2P D 25 3 2P 12 0.1 mol of benzoic acid was dissolved in 500 cm 3 of water. The pH of the solution was found to be 2.6. Which of the following should be added to the solution to form a buffer of maximum buffering capacity? (pKa of benzoic acid is 4.2) A 0.1 mol of NaOH B 0.05 mol of NaOH C 0.1 mol of HCl D 0.05 mol of HCl 13 An excess of silver sulfate was shaken in a solution of sodium sulfate of concentration X mol dm-3 and allowed to reach equilibrium. The undissolved silver sulfate was filtered off and the concentration of silver in the solution was found to be Y mol dm-3. What is the Ksp of silver sulfate? A (X+ 2 Y ) (Y)2 B ( 2 Y ) (Y)2 C (X+Y) (2Y)2 D (X) (Y)2 1315

6   9647/01/TJC Prelim 2013 [Turn Over  14 The reaction between NO and O 2 to give NO2 is exothermic and proceeds by the following two steps. Step 1: NO + O 2 OONO Step 2: NO + OONO  2NO2 It was found that Step 1 is the slow step. Which diagram could represent the reaction pathway diagram for the reaction? A B C D 15 The reaction between substances A and B is found to follow the rate equation. Rate = k[A]m[B] Where k is the rate constant and has units of mol–2dm6s–1. Two experiments to study the kinetics of this reaction were carried out and the data obtained are tabulated below: Experiment Initial [ A] / mol dm–3 Initial [ B] / mol dm–3 Initial rate / mol dm –3 s–1 1 0.040 0.080 S 2 0.020 y ½ S What is the value of y in experiment 2? A 0.020 B 0.040 C 0.160 D 0.320 Energy Progress of reaction Energy Progress of reaction Energy Progress of reaction Energy Progress of reaction 1316

7   9647/01/TJC Prelim 2013 [Turn Over  16 Three elements, J, K, L have physical properties as shown. Substance Melting point of element / oC Solubility of oxide in water Electrical conductivity of chloride in liquid