CJC_H2_CHEM_P2_SOL 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. 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 ANSWER SCHEME

2 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]  Dissolve solid KHC4H4O6 in water until some solid remains undissolved.  Allow solution to stand for few hours (to establish equilibrium).  Filter to remove undissolved solid. The saturated solution of KHC4H4O6