CJC 2022 JC2 H2 CHEM PRELIM P3 QP FINAL COPY

1 9729/03/CJC JC2 Preliminary Examination 2022 [Turn over CANDIDATE NAME CLASS 2T CHEMISTRY 9729/03 Paper 3 Free Response 13 September 2022 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. 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. If additional space is required, you should use the pages at the end of this bookl et. The question number must be clearly shown. Section A Answer all the questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 33 printed pages and 1 blank page. For Examiner’s Use Section A Q1 /15 Q2 /21 Q3 /24 Section B Q4 /20 OR Q5 /20 TOTAL 80 Catholic Junior College JC2 Preliminary Examinations Higher 2

2 9729/03/CJC JC2 Preliminary Examination 2022 Section A Answer all the questions in this section. 1 Chromium is a hard, steel-grey metal with a lustrous appearance. It is valued for its high corrosion resistance and hardness and is commonly used to manufacture alloys such as steel. Chromium plating is sometimes used to give a polished mirror finish to steel. Chromium compounds are also often used as pigments, known as chrome yellow. (a) The following sequence of reactions involving chromium illustrates many of the characteristics properties of transition metals. (i) Solutions of transition metals are frequently coloured. With reference to [Cr(H2O)6]2+,explain fully why it forms a blue solution. [2] (ii) Suggest the identity of the grey -green precipitate formed in the reaction between [Cr(H2O)6]3+ and aqueous sodium hydroxide. With the aid of an equation, explain fully how it is formed. [2] (iii) Chromium(III) ions can also react with iminodiacetate ions (tridentate ligand) to form a chelating complex ion. Draw the structure of the complex ion , showing the shape clearly. [1] (iv) Identify the species present in the yellow and orange solutions. Hence write an equation to show the formation of the species in the orange solution from that in the yellow solution. [2] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… orange solution H2O2(aq) yellow solution chromium metal dilute H2SO4 [Cr(H2O)6]2+ blue solution [Cr(H2O)6]3+ green solution grey-green precipitate [Cr(OH)6]3‒ dark green solution air NaOH(aq) NaOH(aq) dilute H2SO4

3 9729/03/CJC JC2 Preliminary Examination 2022 [Turn over …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ……………………………………………………………………………………………………

4 9729/03/CJC JC2 Preliminary Examination 2022 1 (b) Draw a fully labelled diagram of the experimental set -up used to measure the standard electrode potential of the Cr3+(aq)/Cr(s) half-cell, indicating the direction of electron flow. [3] (c) Chromium is electrolytically deposited on the cathode from a solution containing Cr3+(aq) using inert electrodes. Calculate the volume of oxygen, at room temperature and pressure, produced at the anode when 1.00 kg of chromium is deposited on the cathode. [2] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ……………………………………………………………………………………………………

5 9729/03/CJC JC2 Preliminary Examination 2022 [Turn over 1 (d) Chrome yellow containing Na 2CrO4, has been used for a long time as a yellow pigment in oil paintings. (i) Use the standard redox potentials below to explain why the yellow colour changes when the painting is exposed to an atmosphere containing sulfur dioxide. SO42─ + 4H+ + 2e─ 2H2O + SO2 Eo = +0.17 V CrO42─ + 8H+ + 3e─ Cr3+ + 4H2O Eo = +1.33 V [2] (ii) Suggest why this colour change takes a long time. [1] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… [Total: 15]

6 9729/03/CJC JC2 Preliminary Examination 2022 2 (a) Tartaric acid is a white crystalline diprotic organic acid. It can be synthesi sed from ethene in four steps. Tartaric acid Draw the structures of the intermediates, A, B and C, and give the required reagents and conditions for each step of the conversion. [7] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………