JJC H2 CHEM P2 Qn

[Turn over JURONG JUNIOR COLLEGE 2015 JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS 15S CHEMISTRY 9647/02 Paper 2 Structured Questions 28 August 2015 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet. READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number 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 staples, paper clips, highlighters, glue or correction fluid. Answer all the questions. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. For Examiner’s Use 1 12 2 13 3 10 4 11 5 13 6 13 Penalty (delete accordingly) Lack 3sf in final ans –1 / NA Missing/wrong units in final ans –1 / NA Incorrect Bond linkages –1 / NA Total 72 This document consists of 15 printed pages and 1 blank page.

2 © Jurong Junior College 9647/02/ J2 PRELIMINARY EXAMINATION/2015 Answer all the questions. 1 Planning (P) For Examiner’s Use Calcium hydroxide is an ionic solid that dissolves sparingly in water to form ions. Ca(OH)2 (s)  Ca2+ (aq) + 2OH‒ (aq) It is possible to determine the solubility product of calcium hydroxide by measuring the concentration of Ca 2+ in a saturated calcium hydroxide solution using atomic absorption spectroscopy. Atomic absorption spectrometry is an analytical technique which allows you to measure the concentration of a specific ion in the sample. For this experiment, a sample containing Ca 2+ is placed into the atomic absorption spectrophotometer. In the machine, a specific wavelength which corresponds to calcium is shone onto the sample and the amount of radiation absorbed is measured. The amount of radiation absorbed is expressed as an absorbance value. The higher the concentration of Ca 2+ in the sample, the higher the absorbance value. To determine the concentration of Ca 2+ in a saturated calcium hydroxide solution, a series of known, but different, concentrations of Ca 2+ solutions is prepared. The atomic absorption spectrophotometer is used to measure the absorbance value of Ca 2+ in each solution. A graph of absorbance value against concentration of Ca 2+ is then plotted. This graph is known as a calibration line, which can be used to determine the concentration of Ca2+ in unknown solutions. The experiment is then repeated using a saturated solution of calcium hydroxide. By comparing the absorbance of this solution with the calibration line, the concentration of calcium hydroxide in the saturated solution can be determined. (a) Using the information given above, you are required to write a plan to determine the concentration of Ca 2+ in a saturated calcium hydroxide solution at 25C. You may assume that you are provided with:  0.0500 mol dm 3 Ca 2+ stock solution which should be diluted before the absorbance is measured.  solid calcium hydroxide, Ca(OH) 2;  an atomic absorption spectrophotometer and instructions for its use;  graph paper;  the apparatus and chemicals normally found in a school or college laboratory. Your plan should include details of:  the preparation of a suggested number of diluted Ca 2+ solutions of accurate concentrations from 0.00500 mol dm 3 to 0.0250 mol dm 3 using 25.0 cm 3 graduated flasks;  an outline of how you will obtain the results needed to plot the calibration line;  a sketch of the calibration line you would expect to obtain;  the preparation of a saturated solution of calcium hydroxide;  how the calibration line would be used to determine the concentration of Ca2+ in the prepared saturated calcium hydroxide solution.

3 © Jurong Junior College 9647/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 1 (a) …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... For Examiner’s Use

4 © Jurong Junior College 9647/02/ J2 PRELIMINARY EXAMINATION/2015 1 (a) …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... …...……………………………………………………………………………………... [10] For Examiner’s Use (b) Assuming the concentration of Ca 2+ in the prepared saturated calcium hydroxide solution obtained in (a) is x mol dm3, calculate the solubility product of calcium hydroxide, stating its units. [2] [Total: 12]

5 © Jurong Junior College 9647/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 2 The Strecker synthesis is a route to prepare amino acids. Glycine, 2-aminoethanoic acid, can be prepared from methanal in this way. The reaction is thought to proceed through the following stages. For Examiner’s Use (a) On the structure of methanal given above, circle the atom that is attacked by the ammonia molecule. [1] (b) State the role of ammonia in reaction 1. ……………………………………………………………………………………………. [1] (c) Suggest the structure of compound B. [1] (d) State the type of mechanism that occurs in reaction 3. ……………………………………………………………………………………………. [1] (e) Isoleucine can be produced from compound C using Strecker synthesis. Suggest the structure of compound C. [1]

6 © Jurong Junior College 9647/02/ J2 PRELIMINARY EXAMINATION/2015 2 (f) Reaction 3 in the Strecker synthesis involves the reaction between HCN and CH2=NH. The kinetics of this reaction was determined by monitoring the change in the [HCN] with time using initial concentrations of 0.01 mol dm –3 HCN and 0.2 mol dm–3 CH2=NH. The following graph was obtained. For Examiner’s Use (i) Use the graph above to show that the reaction is first order with respect to [HCN]. …...………………………………………… ……………………………………... …...……………………………………………… ………………………………... [1] (ii) The experimen