HCI H2 Chem 2013 Prelim P2 QP

This document consists of 15 printed pages and 1 blank page. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 12S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper Additional Materials: Data Booklet 9647/02 18 September 2013 2 hours INSTRUCTIONS TO CANDIDATES 1) Write your name, CT group, centre number and index number clearly in the spaces at the top of this page. 2) Answer all questions in the spaces provided in this Question Paper. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. A Data Booklet is provided. Do not use staples, paper clips, highlighters, glue or correction fluid. You may use a calculator. You are reminded of the need for good English and clear presentation in your answers. For Examiner’s Use 1 / 12 2 / 20 3 / 13 4 / 12 5 / 15 Total / 72 Calculator Model: 567

2 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 1 Planning You are provided with a 2.00 mol dm –3 solution of sodium hydroxide and a solution of sulfuric acid of unknown concentration. The enthalpy change of neutralization, Hneut, is the molar enthalpy change for the reaction: H+(aq) + OH–(aq)  H2O(l) A preliminary investigation was carried out to measure the temperature changes, T, when different volumes of the sulfuric acid and sodium hydroxide were reacted together. In one experiment, 10.00 cm 3 of H 2SO4 was reacted with 40.00 cm 3 of NaOH and the temperature change was found to be 11.0 oC. In a second experiment, 20.00 cm 3 of H 2SO4 was reacted with 30.00 cm 3 of NaOH and the temperature change was 18.4 oC. (a) Write a plan to determine the concentration of the sulfuric acid, and a value for the enthalpy change of neutralization, Hneut. Your plan must enable you to plot a graph that includes the data from both of the experiments described above. You may use apparatus normally found in a school laboratory. Your plan should contain the following:  a labelled diagram of the assembled apparatus you would use for measuring the temperature changes, T,  all essential experimental details, including precision of apparatus and volumes of reagents,  a sketch of the graph you expect to obtain, and  an outline of the calculations you would perform to find (i) the concentration, in mol dm–3, of the sulfuric acid (ii) the molar enthalpy change of neutralization, Hneut, in kJ mol– 1 In your calculations, you must clearly define all terms used and simplify your final mathematical expression. You may use letters a, b, … etc, to represent quantities used. 568

3 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. [10] For Examiners Use 1 2 3 4 5 6 7 8 9 10 569

4 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 (b) A student carries out your plan using 1.00 mol dm –3 barium hydroxide instead of 2.00 mol dm –3 sodium hydroxide. Explain whether he would obtain the same results for the concentration of sulfuric acid and for the molar enthalpy change of neutralization, within experimental errors. ……………………………………………………………………………………………....... ……………………………………………………………………………………………....... ……………………………………………………………………………………………....... ……………………………………………………………………………………………....... [2] [Total: 12] For Examiners Use 11 12 570

5 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 2 (a) A pink complex salt A has the molecular formula CoN5H17OCl3 (Mr = 268.4). 1.00 g of A is dissolved in water and the solution is titrated with 0.500 mol d m–3 silver nitrate solution. It is found that 22.40 cm 3 of silver nitrate is required for complete reaction. When the pink solid A is heated, water vapour was evolved to give a purple solid B. A and B have the same coordination number. (i) Calculate the number of moles of free chloride ions per mole of A. (ii) Draw the structure of the complex ion in A. (iii) Suggest the formula of the complex ion in B. …………………………………………………………………………………………......... (iv) Account for the difference in the colour of A and B. …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... [5] 571

6 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 (b) Aqueous hydrogen peroxide is fairly stable, but when a mix ture of a cobalt (II) salt and tartaric acid is added to aqueous hydrogen peroxide, the initially pink solution slowly turns into a green Co(III) species. tartaric acid After a while, oxygen gas is vigorously evolved and the solution turns back to pink again. Both tartaric acid and the cobalt(II) salt are recovered from the solution at the end. (i) Explain the reactions that occurred in the observations that are in italics. …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... (ii) State the role of the cobalt (II) salt and give two pieces of evidence to support your answer. Role of the cobalt(II) salt: ………………………………… Evidence 1: …………………………………………………………………………………………......... …………………………………………………………………………………………......... Evidence 2: …………………………………………………………………………………………......... …………………………………………………………………………………………......... (iii) Write an equation for the overall reaction. …………………………………………………………………………………………......... (iv) With the aid of relevant data in the Data Booklet, show that Co 3+ is not stable in aqueous solution and hence comment on the role of tartaric acid. …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... …………………………………………………………………………………………......... [9] 572

7 © Hwa Chong Institution 2013 9647 / 02 / C2 Prelim 2013 (c) A student wants to plate a leaf with a thin layer of cobalt. He first coated the le