CJC H2 CHEM P2 QP Prelim

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS 2T CHEMISTRY 9647/02 Paper 2 Structured Questions Monday 24th August 2015 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class in the spaces provided above. Write in dark blue or black pen in the spaces provided, on the Question Paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] 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 remind ed of the need for good English and clear presentation in your answers. The number o f marks is given in brackets [ ] at the end of each question or part of the question. This document consists of 18 printed pages. For Examiner’s Use Paper 1 40 Paper 2 Q 1 12 Q 2 15 Q 3 15 Q 4 15 Q 5 15 72 Paper 3 Q 1 20 Q 2 20 Q 3 20 Q 4 20 Q 5 20 80 Total 192 [Turn over

2 [Turn over 1 Planning (P) Cream of tartar (potassium hydrogen tartrate, KHC 4H4O6) is one of the ingredients in baking powder which is used to make cakes rise. Potassium hydrogen tartrate is a weak acid that is not very soluble in water. KHC4H4O6(s) ⇌ K+(aq) + HC4H4O6 –(aq) The HC 4H4O6 –(aq) ion contains one acidic hydrogen, so the quantity of potassium hydrogen tartrate in solution can be determined by titration with a base. HC4H4O6 –(aq) + OH–(aq)  H2O(l) + C4H4O6 2–(aq) You are to design an experiment to determine the solubility of potassium hydrogen tartrate in two solvent systems: pure water and 0.100 mol dm–3 potassium chloride. In addition to the standard apparatus available in a school laboratory, you are provided with the following materials:  potassium hydrogen tartrate  distilled water  methyl orange indicator  phenolphthalein indicator  standard sodium hydroxide solution (a) Write an expression for the solubility product, Ksp, of potassium hydrogen tartrate, stating its units. …………………………………………………………………………………………………. [1] (b) When a solution is saturated, the undissolved solid is in equilibrium with its aqueous solution. X(s) + aq ⇌ X(aq) Describe how you would prepare a saturated solution of potassium hydrogen tartrate at room temperature. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. [3] For Examiner’s Use

3 9647/02/CJC JC2 Preliminary Exam 2015 (c) The concentration of a saturated solution of potassium hydrogen tartrate may be determined by titration with standard sodium hydroxide. (i) Given that, at room temperature, Ksp of potassium hydrogen tartrate has a numerical value of 6.27 × 10 –4, suggest an appropriate concentrat ion of the standard sodium hydroxide solution to be prepared. Show your working. (ii) Name the indicator used in this titration. ……………………………………………………….………………………………….. [3] (d) Describe what further experiments you would carry out to determine the solubility of potassium hydrogen tartrate in 0.100 mol dm–3 potassium chloride. State clearly the volume of solution used and the expected observation. …...…………………………………………………………………………………………….. …...…………………………………………………………………………………………….. ……………...………………………………………………………………………………….. ………………………...……………………………………………………………………….. …………………………………...…………………………………………………………….. ……………………………………………...………………………………………………….. ……………………………………………………………………………...………………….. State and explain how the titration result of this further experiment would compare with that of the solution prepared in (b). …...…………………………………………………………………………………………….. ………………………………………………………………………………………...……….. ………………………………………………………………………...……………………….. [5] [Total: 12] For Examiner’s Use [Turn over

4 9647/02/CJC JC2 Preliminary Exam 2015 2 Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen. It is present in all forms of carbon -based life, and in the human body. This abundance, together with the unique diversity of or ganic compounds , makes this element the chemical basis of all known life. (a) (i) Organic compound P contains only the elements carbon, hydrogen and oxygen in the following composition by mass: C, 40 %; H, 6.7 %. Calculate the empirical formula of P. (ii) When a 0.102 g sample of compound P was vapourised in a suitable apparatus, the vapour occupied 59 cm3 at 150 °C and 101 kPa. Calculate the relative molecular mass of compound P, and hence determine its molecular formula. (iii) Compound P gives a silver mirror with Tollens’ reagent. Draw the displayed formula of compound P. [5] For Examiner’s Use

5 9647/02/CJC JC2 Preliminary Exam 2015 (b) Starch is another organic compound consisting of carbon, hy drogen and oxygen. The hydrolysis of starch into simpler sugars can be catalysed by the enzyme amylase. Amylase is present in the saliva of humans and acts as a biological catalyst in the digestion of starch. (i) A few experiments are carried out with different concentrations of starch solution and the initial rates of hydrolysis in the presence of the enzyme, amylase, are measured. The graph below shows how the initial rates of the hydrolysis reaction in the presence of amylase vary with the concentrations of starch solution. Explain the relationship between the concentration of substrate and the initial rate of reaction, making reference to the order of reaction with respect to the substrate concentration. ………………………………………………………….………………………………. ………………………………………………………….………………………………. .…………………………………………………………………………………………. ………………………………………………………….………………………………. .…………………………………………………………………………………………. .…………………………………………………………………………………………. .…………………………………………………………………………………………. (ii) On the same graph in (b)(i), sketch another graph to show how the initial rates will vary with the concentrations of starch solution if the concentration of amylase is halved. Label this graph as (ii). [3] [starch] initial rate For Examiner’s Use [Turn over

6 9647/02/CJC JC2 Preliminary Exam 2015 (c) Allotropes are pure forms of the same element that differ in structure. There are several allotropes of carbon such as graphite and diamond. A mixture of carbon dioxide reacts with hot graphite according to the equation below: CO2(g) + C(s) ⇌ 2CO(g) H = +170 kJ mol–1 The mixture was allowed to reach dynamic equilibrium at 817 °C in a 2 dm 3 closed vessel. The amount of CO2, C and CO at equilibrium is given below. CO2 C CO Equilibrium amount / mol 0.1 0.7 1.7 (i) What do you understand by the term dynamic equilibrium? …........………………………………………………………………………………….. …….…………………………………………………………………………………….. …….…………………………………………………………………………………….. ….……………………………………………………………………………………….. (ii) Write an expression for the equilibrium constant, Kc, of this reaction, stating the units. …………………………………………………………………………………………... (iii) Use the data given and your answer to (c)(ii) to calculate a value for Kc of this reaction. For Examiner’s Use

7 9647/02/CJC JC2 Preliminary Exam 2015 (iv) State, with reasoning, the effect on the position of equilibrium if (I) the total volume of the system is increased at 817 °C. ……………………………………………………………………………………. ……………………………………