DHS H2 Chem 2013 Prelim P2 Soln

_______________________________________________________________________________________________ This question paper consists of 16 printed pages and 1 blank page. © DHS 2012 [Turn over Name: Suggested Solutions Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY 9647/02 Paper 2 Structured 19 September 2013 2 hours Additional Materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page. 2 Answer all questions. 3 Write your answers in the spaces provided on the question paper. 4 A Data Booklet is provided. 5 The number of marks is given in brackets [ ] at the end of each question or part question. 6 You may use a calculator. FOR EXAMINER’S USE Question No. 1 2 3 4 5 6 Total % Marks 12 15 9 10 15 11 [72] 510

2 © DHS 2013 9647/02 [Turn over Answer all questions in the space provided. 1 Planning Solubility is defined as the mass of solid that will dissolve in and just saturate 100 g of solvent at a particular temperature. When potassium nitrate dissolves in water, the temperature of the solution decreases as the enthalpy change of solution is endothermic. You are to plan an experiment to investigate how the solubility of potassium nitrate varies with temperature. The units of solubility are grams per one hundred grams of water (g/100 g of water). (a) (i) Predict how the solubility of potassium nitrate will change if the solution temperature is increased. By Le Chatelier’s principle, when temperature is increased, the equilibrium will shift to the right to absorb the excess heat and favour the endothermic reaction. Hence the solubility will increase with increasing temperature. (ii) Display your prediction in the form of a sketch, labeling clearly the y-axis. solubility 25 temperature/ °C [3] 511

3 © DHS 2013 9647/02 [Turn over (b) You are to design an experiment to test your prediction in (a). (i) Given that the solubility of potassium nitrate at 70 °C = 11.3 mol dm–3 Calculate the maximum mass of potassium nitrate that can be dissolved in 100 g of water at 70 °C. Maximum mass = (100/1000) x 11.3 x (39.1 x 14.0 x 3(16.0)) = 114 g (ii) Describe how you would carry out the experiment. You should • include the apparatus used; • ensure a wide range of results suitable for analysis by graph; • decide on the amount of water and potassium nitrate to be used; • describe how the temperature of the solution is to be maintained. You may also assume that standard laboratory apparatus are available. 1. Measure approximately 120 g of potassium nitrate using a weighing balance. [1] Measure 100 ml of water using a measuring cylinder/burette and transfer the water to a 250 cm3 beaker. (total mass of solid + water should not exceed 250 g, mass of solid added