NJC_Prelim_P2

NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions 8872/02 17 September 2009 2 hours For Examiner’s Use Section A 1 2 3 4 5 Section B B6 B7 B8 READ THE INSTRUCTION FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions . Section B Answer any two questions. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Total This question paper consists of 13 printed pages (including this page).

2 Section A Answer all the question s in this section in the spaces provided. 1 5.00 g of impure iron solid was dissolved in an excess of sulfuric acid and the resulting solution containing Fe2+ was made up to 250 cm 3. 10.0 cm3 of this solution was titrated against a solution of KMnO 4 of concentration 0.01 mol dm 3. It was found that 24.00 cm3 of KMnO4 was required. (a) Suggest a reason why an indicator was not required for this titration. …………………………………………………………………………………......... ……………………………………………………………………………………….. ……………………………………………………………………………………….. [1] (b) Write a balanced redox equation for the reaction between Fe 2+ and MnO4 . …………………………………………………………………………………......... [2] (c) A student claims that the percentage purity of iron in the sample is 33.5%. Justify if the statement made by the student is true. [3] [Total: 6] [Turn Over

3 2 The graphs below shows the rate of hydrolysis of ethyl ethanoate, CH3COOC2H5 in an acidic medium. The reaction was followed twice with different concentrations of HCl and the following results were obtained. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0 50 100 150 200 250 (a) Using the graphs, determine the order of reaction with respect to both ethylethanoate and HCl. (b) Deduce the rate equation and calculate the value of the rate constant, giving its units. (c) On the same axis above, sketch the graph when the experiment is repeated using 0.008 mol dm 3 of ethylethanoate and 0.15 mol dm3 HCl. [Total: 7] [ethyl ethano ate]/ mol dm3 [HCl] = 0.10 mol dm3 [HCl] = 0.15 mol dm3 Time/min [Turn Over

4 3 Methanol is a possible alternative to hydrocarbons as a liquid fuel. (a) Given that the enthalpy of combustion of methanol is –715 kJ mol –1, calculate the mass of methanol that should be burnt in order to boil 1000 cm 3 of water starting from an initial temperature of 20.0 °C. Assume that 50% of the heat obtained f