SAJC 2024 Prelim P4 Answers

1 Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION CHEMISTRY Paper 4 Practical 9729/04 15 August 2024 2 hours 30 minutes Additional Materials: Qualitative Analysis Notes Shift Laboratory For Examiner’s Use 1 2 3 4 Total This document consists of 18 printed pages including this page. READ THESE INSTRUCTIONS FIRST. Write your name and class on all the work you hand in. Give details of the practical shift and laboratory in the boxes provided above. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in the brackets [ ] at the end of each question or part question. 13 17 15 10 55

2 Answer all the questions in the spaces provided. 1 Identification of unknown cation, anion and acids FA 1 is a salt which contains a cation and an anion. FA 2 is an aqueous mixture of two acids. The possible acids are hydrochloric acid, nitric acid and sulfuric acid. You will perform tests to identify the ions in FA 1 and determine which acids are present in FA 2. Test and identify any gases evolved, unless otherwise stated. If there is no observable change, write no observable change. (a) (i) Carry out the following tests and record your observations in Table 1.1. Table 1.1 tests observations 1 Add approximately one spatula of FA 1 in a boiling tube and heat strongly for about 1 minute, then leave to cool. Do not test for gas. White solid turned yellow upon strong heating. Yellow solid turned white again upon cooling. Note: Some students might have also observed colourless droplets forming on the top of the boiling tube. 2 To an approximately 2 cm depth of FA 2 in a test tube, carefully add approximately one spatula of FA 1. Keep this solution for use in 1(b)(i). White solid dissolved to form colourless solution. Effervescence observed. Gas forms white ppt with limewater. Gas is CO2. [4]

3 (ii) Identify the anion in FA 1 and write an ionic equation to explain how you deduced its identity, using your observations in Table 1.1. …………………………………………………………………………………………… …………………………………………………………………………………………… [1] Anion is CO32− 2H++ CO32− → CO2 + H2O (b) (i) Devise and perform a series of simple tests on the solution from Test 2 in (a)(i) to identify the cation in FA 1. Your tests should be based on the Qualitative Analysis Notes on pages 17 to 18 and should only use the bench reagents provided. Record your tests and observations in the space below. Test Obs