NYJC 2024 H2 Chem P4 QP

H NANYANG JUNIOR COLLEGE JC2 PRACTICAL PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS CENTRE NUMBER S INDEX NUMBER CHEMISTRY 9729/04 Paper 4 Practical 14 August 2024 2 hour 30 minutes Candidates answer on the Question Paper Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and class on all the work you hand in. Give details of the practical shift and laboratory, where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs Do not use staples, paper clips, 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. Shift You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 23 and 24. Laboratory 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 / 16 2 / 16 3 /12 4 / 11 Total /55 This document consists of 20 printed pages and 4 blank pages.

2 H2 Chemistry 9729/04 NYJC J2/24 PX Answer all questions in the space provided. 1 An investigation of a gemstone Spinel minerals form crystals that are often used as gemstones. The general formula of a spinel mineral is AB2O4, where A and B are different metal ions. The presence of different combinations of metal ions accounts for the range of colours found in these gemstones. One example of a spinel gemstone is hercynite, which is blue-green in colour. As they are essentially composed of metal oxides, spinel crystals may be reacted with strong acids to form solutions containing salts of the metal ions present. The rarity and high cost of spinel gemstones, however, prohibit the preparation of such solutions for this task. The FA 1 solution you are supplied with is a mixture of two salts. It is intended to duplicate a solution that could have been produced by reacting hercynite crystals with a strong mineral acid. Consequently, non-metal ions are also present in FA 1. FA 1 is a solution containing the metal ions, A and B, together with non-metal ions. FA 2 is a solution of sodium carbonate, Na2CO3. Solid FA 3 is granulated zinc. You will perform tests to identify the metal ions, A and B, present in FA 1. You are not expected to identify the anions. You are advised to consider the general formula of the spinel minerals, AB2O4, and the likely oxidation states of the metal ions, A and B, before you start this experiment. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. Test and identify any gases evolved. (a) Carry out the following tests. Carefully record your observations in Table 1.1.

3 H2 Chemistry 9729/04 NYJC J2/24 PX Table 1.1 test observations 1 Test the FA 1 solution using Universal Indicator paper. 2 Using a measuring cylinder, transfer 10 cm 3 of FA 1 to a clean boiling tube. Use a dropping pipette to transfer 1 cm 3 of FA 2 to the boiling tube. Mix the contents of the boiling tube thoroughly. Repeat the transfer of 1 cm 3 of FA 2 with thorough mixing of the contents in the boiling tube until all of the FA 2 is used up. 3 Place about 2 cm 3 of FA 1 into a test-tube. Carefully add sodium hydroxide, dropwise with shaking, until no further changes are seen. Swirl and filter the mixture, collecting the filtrate in a clean boiling tube. Keep the filtrate for use in Test 6. Wash the residue thoroughly with deionised water. Discard the washings. Keep the residue for use in Test 4.

4 H2 Chemistry 9729/04 NYJC J2/24 PX test observations Note: When aqueous potassium manganate(VII) is added in Test 4, the endpoint is a permanent pale pink colour. 4 Transfer a spatula load of the residue collected in Test 3 to a clean test-tube. Carefully add hydrochloric acid, dropwise with shaking, until no further changes are seen. Add aqueous potassium manganate( VII), dropwise with shaking, until the end -point is reached. Record the number of drops of aqueous potassium manganate(VII) you have added to reach the end-point. Keep this mixture for use in Test 5. 5 To the final mixture in Test 4, add one piece of FA 3 . Gently warm the mixture and set aside for a few minutes. From time to time, observe the mixture. While you are waiting, continue with Test 6. When no further changes are observed, decant the solution into a second test-tube. Add a few drops of aqueous potassium manganate(VII) to the second test-tube, with shaking.

5 H2 Chemistry 9729/04 NYJC J2/24 PX test observations 6 Place about 1 cm 3 of the filtrate collected in Test 3 in a clean test -tube. Carefully add hydrochloric acid, dropwise, until no further change is seen before you shake the mixture. This mixture is then use for Test 7. Note: You should NOT do the following test. Observations have been recorded for you. 7 Place about 1 cm 3 of the final mixture in Test 6 in a clean test -tube. Add aqueous ammonia, dropwise with shaking, until no further change is seen. white ppt. insoluble in excess [8] Obs points marks (b) By considering your observations in Tests 1 and 2 , suggest an explanation for the observations in Test 2 in terms of the chemistry involved. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [2]

6 H2 Chemistry 9729/04 NYJC J2/24 PX (c) (i) By considering your observations in Test s 3, 6 and 7, i dentify the metal - containing complex ion present in the filtrate collected in Test 3. ……………………………………………………………………………………… [1] (ii) Identify the residue collected in Test 3. ……………………………………………………………………………………… [1] (iii) FA 1 is intended to duplicate a solution that could have been produced by dissolving hercynite in a strong acid. Suggest a formula for hercynite. ……………………………………………………………………………………… [1] (d) Explain the following reactions involving the metal ions in the reaction mixture used in Test 5. • reaction between granulated zinc and resultant mixture from Test 4 • reaction between solution in the second test -tube and aqueous potassium manganate(VII) …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [1] (e) Explain, in terms of the chemistry involved, and with the aid of relevant equations, your observations in Test 6. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………. [2] [Total: 16]

7 H2 Chemistry 9729/04 NYJC J2/24 PX 2 Determination of the molar enthalpy change of a reaction by an indirect method It is not possible to measure experimentally the enthalpy change, H1, for the following reaction as it does not take place in the laboratory. equation 1 Na2CO3(s) + CO2(g) + H2O(l) → 2NaHCO3(s) H1 Sodium carbonate and sodium hydrogencarbonate each react with hydrochloric acid. equation 2 Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g) H2 = −36 kJ mol−1 equation 3 NaHCO3(s) + HCl(aq) → NaCl + CO2 + H2O H3 In this question, you will perform an experiment to determine a value for H3. You will use the results of the ex