NYJC_H2_CHEM_P2_ANS Prelim

1 NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME Answers CLASS TUTOR’S NAME CHEMISTRY 9647/02 Paper 2 Structured Questions 19 September 2011 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. 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 10 3 12 4 20 5 18 Total 72 This document consists of 19 printed pages and 1 blank page. [Turn over

2 1 Planning (P) There are four colourless solutions, labelled as A1, A2, B1 and B2. You are told that A1 and A2 could be 1.0 mol dm –3 H 2SO4 or 2.0 mol dm –3 H 2SO4. B1 and B2 are either 1.0 mol dm–3 NaOH or 1.0 mol dm–3 Ba(OH)2. You are required to plan a simple experiment to identify A1, A2, B1 and B2. You are provided with 200 cm 3 of each solution, a thermometer polystyrene cup common apparatus in the laboratory No pH indicators are provided. For Examiner’s Use (a) Suggest how we can first identify Ba(OH) 2. Write an equation (with state symbols) to explain your answer. Add a few drops of A1 (or A2) to 2 cm 3 of B1. Repeat this with B2. The solution which gives a white precipitate is Ba(OH)2. Ba(OH)2 (aq) + H2SO4 (aq)  BaSO4 (s) + 2H2O ( l ) [2] (b) Write an equation for the reaction betw een sodium hydroxide and sulfuric acid. 2NaOH (aq) + H2SO4 (aq)  Na2SO4 (aq) + 2H2O (l) [1] (c) Outline the steps you will take to determine the identities of A1 and A2, using the sodium hydroxide solution. Step 1: Using a measuring cylinder, add 20 cm 3 of A1 into the polystyrene cup provided and record its initial te mperature. Using another measuring cylinder, measure 80 cm3 of NaOH and record its initial temperature. Step 2: Add the 80 cm 3 of NaOH into the polystyrene cup containing A1, stir with the thermometer and record the highest temperature reached. Rinse the cup. Step 3: Repeat steps 1 and 2, this time replacing A1 with A2. [Accept any specific volume suggested by student, but volume of NaOH should be 4 times of A2/A1 and total volume of mixture should be between 50-100 cm3.] [3]

3 (d) Let T1 be the temperature change for the reaction between A1 and NaOH(aq) and T2 be the temperature change for the reaction between A2 and NaOH(aq). Illustrate how the identities of A1 and A2 can be deduced from the