NJC H2 Chem 2013 Prelim P2 QP

NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Answer on the Question Paper. Additional Materials: Data Booklet 9647/02 Wed 4 Sept 2013 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black ink in the spaces provided. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /16 3 /14 4 /6 5 /8 6 /16 Total /72 This document consists of 20 printed pages and 0 blank page. 104

NJC/H2 Chem/02/2013 [Turn over 2 1 Planning (P) Calcium iodate( V), Ca( IO3)2, is slightly soluble in water, approximately 4.6 g dm‒3 at 25°C. The molar enthalpy of a solution is defined as the enthalpy change when one mole of the solid dissolves in water. [ Mr of Ca(IO3)2 : 390.1] (a) (i) Predict and explain how the solubility of calcium iodate(V ) in water changes as the temperature is increased. Ca(IO3)2 (s) Ca2+ (aq) + 2IO3 ‒ (aq) ΔHsol > 0 ………………………………………………………….……………………………………. ………………………………………………………………..……………………………… ………………………………………………………………….……………………………. ………………………………………………………………………..……………………… (ii) Display your prediction in the form of a sketch graph between 0°C and 100°C. Label the axes with units and give numerical values to ensure that the line clearly shows the solubility at 25°C. [3] (b) You are to conduct an experiment to determine as accurately as possible the concentration of a saturated solution of calcium iodate(V). You may assume you are provided with the following:  FA1: 250 cm3 suspension of calcium iodate(V)  FA2: 1.00 mol dm‒3 of potassium iodide, KI  FA3: 1.00 mol dm ‒3 sodium thiosulfate, Na2S2O3  FA4: 1.00 mol dm ‒3 hydrochloric acid, HCl For Examiner’s Use 105

NJC/H2 Chem/02/2013 [Turn over 3  Deionised water  Indicators commonly found in the laboratory  the apparatus normally found in a school or college laboratory (i) Given that acidified iodate(V ) reacts with iodide to form iodine, IO3 ‒ (aq) + 5I‒ (aq) + 6H+(aq)  3I2(aq) + 3H2O(l) With the aid of an equation, suggest how the amount of iodine produced in this reaction can be determined using only the solutions given. ………………………………………………………………………………………….….. ………………………………………………………………………………………...…… (ii) Write