SAJC H2 CHEM P2 QNS Prelim

1 [Turn Over Name: Class: ST ANDREW’S JUNIOR COLLEGE JC 2 Preliminary Exam Chemistry Higher 2 9647/02 1 September 2015 Paper 2 2 hours Candidates answer in the spaces provided on the question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen. 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: Question Marks 1 2 3 4 5 Total (72 marks) This document consists of 25 printed pages (including this page) and 1 blank page.

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3 [Turn Over 1 Planning Calcium hydroxide, Ca(OH) 2, is sufficiently insoluble in water such that it forms a saturated Ca(OH)2 solution, as shown in the following equation: Ca(OH)2 (s) Ca2+ (aq) + 2OH– (aq) The following experiments were carried out to determine the solubility product of calcium hydroxide. Differe nt volumes of NaOH and water were added separately to different dry conical flasks according to the following table. Experiment Vol of NaOH / cm3 Vol. of water / cm3 [ OH– ] in the saturated solution/ mol dm–3 1 5.00 45.00 0.04 2 10.00 40.00 0.03 3 15.00 35.00 0.02 4 20.00 30.00 0.01 5 25.00 25.00 0.001 Excess solid calcium hydroxide was added to each conical flask before it was stoppered and shaken for a few minutes. The solution was filtered and titrated to determine the concentration of hydroxide ions in the saturated solution. (a) On the grid provided, plot a graph using the values from the above table. [1] [ OH– ] in the saturated solution/ mol dm–3 Volume of NaOH / cm3

4 [Turn Over 1 (b) Explain why the concentration of hydroxide ions in the saturated solution decreases when more sodium hydroxide is added to the conical flask. ………………………………………………………………………………………….………. ………………………………………………………………………………………….………. ………………………………………………………………………………………….………. [1] (c) Explain why dry conical flasks needs to be used to prepare the saturated solution. ………………………………………………………………………………………….………. ………………………………………………………………………………………….………. [1] (d) Write the Ksp expression for Ca(OH)2, stating its units. [2] (e) Using the graph plotted, calculate the numerical value of Ksp of Ca(OH)2. [2]

5 [Turn Over 1(f) Using the information above, you are required to write a plan to  prepare a saturated solution of calcium hydroxide and  determine the concentration of hydroxide ions in the saturated solution in experiment 1. You may assume that you are provided with:  solid calcium hydroxide  1 mol dm–3 aqueous hydrochloric acid;  the apparatus normally found in the college laboratory Outline how you would carry out experiment 1. Your plan should include details of :  the apparatus you would use, bearing in mind the levels of precision they offer;  Indicate the colour change at the end point with your chosen indicator. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….…………………………………………………………………..

6 [Turn Over 1(f) ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. ………………………………….………………………………………………………………….. [5] [Total: 12 marks]

7 [Turn Over 2 The Cobasys’ NiMH batteries supersede the performance of other rechargeable batteries due to its high performance, lighter weight and longer life cycle. It uses a metal hydride alloy as one of the electrode. Today, NiMH batteries are used pervasively in many application s such as cell phones and hybrid cars. (a) The standard electrode potential of the NiOOH (aq) / Ni(OH) 2 (s) system in an alkaline medium is +0.41 V. Draw a fully labelled diagram of how you would determine the standard electrode potential of the NiOOH (aq) / Ni(OH)2 (s) system. [3] (b) The equation at the anode is MH + OH– M + H2O + e– Construct the half equation that occurs at the cathode in an alkaline medium , and the overall equation for the Cobasys’ NiMH cell during discharging. Cathode: ………………………………………………………………………………….………. Overall: ………………………………………………………………………………….………… [2]

8 [Turn Over 2 (c) The table below shows the standard electrode potential of different types of metal hydride, XH, YH, ZH that could possibly be used as an anode in the Cobasys’ NiMH cell. Metal Hydride, MH Eθ value/ V XH + 0.37 YH + 0.58 ZH – 0.42 (i) State which metal hydride is the most effective to be used in the Cobasys’ NiMH cell. ……………………………………………… [1] (ii) Explain your answer in (c)(i). ………………………………………………………………………………………….…… ………………………………………………………………………………………….…… [1] (d) Explain the effect, if any, on the e.m.f. of the cell on adding aqueous H2SO4 to the anodic half cell during discharging. ………………………………………………………………………………………….…… ………………………………………………………………………………………….…… ………………………………………………………………………………………….…… ………………………………………………………………………………………….…… [2]

9 [Turn Over 2 (e) The Cobasys’ NiMH cell can be recharged when the power is depleted. (i) Write the overall equation for the reaction upon charging. ………………………………….…………………………………………………………… [1] (ii) To charge the Cobasys’ NiMH cell completely, a continuous current of 2.0 A for two hours is required. Calculate the minimum mass of the Ni(OH) 2 that would have to be present initially. [3] [Total: 13 marks]

10 [Turn Over 3 Two cations and one anion are mixed together to form a brownish green solution, FA 1. A series of tests is carried out in the reaction scheme as shown.