NYJC_H2_Chemistry_P2_Answers Prelim

H2 Chemistry 9647/02 NYJC J2/14 PX [Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME Teachers’ Mark Scheme CLASS 1 3 INDEX NO. TUTOR CHEMISTRY 9647/02 Paper 2 Structured 22 September 2014 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class 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 questions in the spaces provided. 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 P /12 2 /26 /60 3 /18 4 / 6 5 /10 This document consists of 17 printed pages and 0 blank page.

2 H2 Chemistry 9647/02 NYJC J2/14 PX For Examiner's Use Answer all questions in the spaces provided. 1 Planning (P) H A is a solid monoprotic acid. It is a weak organic acid with p K a value of 4.15. Its solubility in water is only about 3.44 g dm 3 under normal laborator y temperature. Its sodium salt, NaA (Mr = 144.0), is soluble in water. FA 1 is a fine powder of HA with NaA as an impurity. FA 2 is 0.975 mol dm 3 aqueous sodium hydroxide. The reaction between H A and NaOH(aq) is exothermic. A preliminary experiment was conducted using 2.50 g of FA 1 and 40 cm 3 of FA 2. The sample of FA 1 dissolved completely to give a temperature rise of 6.3 C. The experiment was repeated two more times with different masses of FA 1. FA 1 dissolved completely when 5.00 g were used but only partially when 5.50 g were used. To determine the percentage by mass of H A in FA 1, m g of FA 1 can be reacted with V cm 3 of FA 2 to obtain the temperature rise, T. By repeating the experiments for different sets of m and V values, a suitable graph can be plotted to determine the set of m and V values required for complete neutralisation (the end-point). (a) If a series of five experiments is to be carried out, suggest suitable masses and volumes so that T is at least 10 C for each experiment. Show relevant calculations. Experiment I II III IV V Mass of FA 1, m / g Volume of FA 2, V / cm3 Minimum mass of FA1 = 50.23.6 10  = 3.97 g [1] m / g = 4.00, 4.50, 5.00, 5.50, 6.00 or other suitable sets V / cm3 = 40.00 (constant) [1] 2/3 points on either side of end-point Note: For 4.00-5.00 g, NaOH is in excess; 5.50 –6.00 g HA is in excess. [1] [3]

3 H2 Chemistry 9647/02 NYJC J2/14 PX [Turn over For Examiner's Use (b) Using the information given above, you are required to write a plan to determine the temperature rise for Experiment I. You may assume that