MI H2 Chem 2012 Prelim P2 QP

Class Adm No Candidate Name: 2012 Preliminary Examination II Pre-university 3 H2 CHEMISTRY 9647/02 Paper 2 18 Sept 2012 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST 1. Do not turn over this question paper until you are told to do so. 2. Write your name, class and index number in the spaces provided at the top of this page. 3. Write in dark blue or black pen in the spaces provided on the Question Paper. 4. You may use a soft pencil for any diagrams or graphs. 5. DO NOT use paper clips, highlighters, glue or correction fluid or tape. 6. Answer ALL the questions. 7. Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place in the case of Mr and Ar, unless a different level of accuracy is specified in the question. 8. The number of marks is given in brackets [ ] at the end of each question or part question. 9. You are reminded of the need for clear presentation in your answers and to show all working in calculations. 10. The use of a calculator is expected, where appropriate. Paper 2 Question No 1 2 3 4 5 6 (12m) (9m) (10m) (16m) (10m) (15m) Marks Obtained 72 This question paper consists of 16 printed pages. [Turn over

2 1 Planning The benzenediazonium ion, C6H5N2+, reacts with water as shown in the equation. C6H5N2+ (aq) + H2O (l) ® C6H5OH (aq) + N2 (g) + H+ (aq) At temperatures below 10 ºC, the reaction is very slow. However, nitrogen gas is evolved at a measureable rate at temperatures of 20 ºC and above. In this experiment, you are provided with an aqueous solution containing 0.100 mol dm-3 of the benzenediazonium ion at a temperature below 10 ºC. You are required to design an experiment to deduce the order of reaction with respect to C6H5N2+ of an aqueous solution at 20 ºC and an atmospheric pressure of 101 kPa. (a) Define the term order of reaction. [1] ................................................................................................................................................ ................................................................................................................................................ (b) Outline the steps you would take to determine the order of reaction with respect to C6H5N2+ (aq) at 20 ºC. In your plan, include the following details: - a suitable volume of C6H5N2+ (aq) used, - measurement(s) to be taken, - plotting of a suitable graph, if any. [5]

[Turn over 3 (c) Draw a labelled diagram of the experimental set-up. [You may assume that you are given common apparatus found in a school laboratory.] [2] (d) Describe how you will use the results obtained to determine the order of reaction with respect to C6H5N2+ (aq). [2] ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (e) Identify one potential hazard in this experiment and suggest the safety precaution you would take to overcome this. [2] ................................................................................................................................................ ................................................................................................................................................ [Total: 12 marks]

4 2 (a) A lower secondary Science student described an atom of Silicon as having ‘fourteen bees buzzing around a space the size of a football stadium, as though they are being trapped.’ (i) Explain using Chemistry concepts, what do the bees in the description represent and what stopped the bees from flying away from the stadium? ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (ii) The teacher commented that the student’s description of Silicon was incomplete. What is missing from the student’s description of Silicon? ................................................................................................................................................ ................................................................................................................................................ (iii) 28Si, 29Si, 30Si are isotopes of Silicon. Explain why isotopes of Silicon undergo identical chemical reactions? [3] ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................

[Turn over 5 (b) Amongst all the elements in Period 3 of the periodic table, Silicon has the highest melting point. Sketch a graph to illustrate the trend of the melting points of elements in Period 3. Explain your sketch. [4] ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ .............................