SAJC_H2_CHEM_P2 Prelim

1 Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Chemistry Higher 2 9647/02 Paper 2 19 September 2011 2 hours Candidates answer in the spaces provided on the question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen. 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 reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use: Question Marks 1 2 3 4 5 Total This document consists of 13 printed pages including this page.

2 1. Planning (P) FA 1 is a solution of sulphuric acid, H2SO4, of concentration approximately 1 mol dm-3. FA 2 is a solution of 1.50 mol dm-3 sodium hydroxide, NaOH When sulphuric acid neutralises sodium hydroxide, water is produced. H2SO4 + 2NaOH  Na2SO4 + 2H2O The neutralisation process is exothermic, that is, gives out heat, and the amount of heat produced changes with the amount of water produced. From the temperature rise in various experiments, the actual concentration of H2SO4 in FA 1 can be determined. (a) Calculate the approximate temperature rise, T, when 10 cm3 of FA 1 and 40 cm3 of FA 2 were mixed. In your calculations, you are to assume specific heat capacity of the mixture = 4.18 J cm-3 K-1 standard enthalpy change of neutralisation (per mole of water) = – 57.4 kJ mol-1 T: ………………………. [3] (b) Fill in the table below, the approximate temperature rise when various volumes of FA 1 and FA 2 were mixed. In each case, the total volume of mixture is 50 cm3. Volume of FA 1 / cm3 10 20 30 40 Volume of FA 2 / cm3 40 30 20 10 Temperature rise, T / oC [2]

3 1. (c) With the help of (b), describe the steps you would carry out to determine the exact concentration of H2SO4 in FA 1. [3] (d) Identify one source of error in your procedure and explain how you would minimise the error. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [2] (e) From the graph of temperature rise against volume of FA 1, show how you would treat the data in order to determine the actual concentration of H2SO4 in FA 1. [2] [Total: 12] [Turn over

4 2. The preparation of iodo -compounds can be prepared from alcohols and phosphorus tri-iodide, PI3. However, PI3 are not readily available. Hence, it is generated in situ from red phosphorus and iodine. The following equations and steps show how iodoethane can be prepared. 2P + 3I2 2PI3 ΔH = -92 kJ mol-1 3CH3CH2OH + PI3