JJC_H2_CHEM_P2_Qn(1)

[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 i