2022 MI H2 Chem Prelim Paper 2 - Answer

Class Adm No Candidate Name: This question paper consists of 16 printed pages and 2 blank pages. 2022 Preliminary Exams Pre-University 3 H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 14 Sep 2022 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. The use of an approved scientific calculator is expected, where appropriate. 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. Question 1 2 3 4 5 Total Marks 20 13 24 9 9 75

2 Answer all questions in the spaces provided. 1 Many household tools are made from stainless steel as it is highly resistant to corrosion and rust. Stainless steel contains iron, chromium, manganese, nickel, molybdenum, silicon and carbon which interacts with oxygen from water and air to form oxides. Of these elements, chromium has the highest resistance to corrosion. Despite the high resistance, rusting still occurs in a humid environment. A ‘Do -it-Yourself’ (DIY) kit has been launched in the market to remove rust from household tools and the set-up is shown in Figure 1.1. Figure 1.1 (a) (i) State if the iron sheet is the anode or the cathode. [1] anode (ii) Use of Data Booklet is relevant to this question. State and explain the observations found at the iron sheet electrode. [2] The iron sheet will becomes smaller. (;) Fe → Fe2+ + 2e Eº = –0.44 V 2H2O → O2 + 4H+ + 4e- Eº = +1.23 V (;) Since EºFe2+/Fe is more negative than Eº(O2/H2O), Fe is preferentially oxidized to Fe2+. (;) (iii) Suggest why carbonate ions from Na2CO3 electrolyte cannot be oxidised at the anode. [1] Carbon in carbonate is at the maximum oxidation state of +4 or the electrode potential involving carbonate ion is very positive. Rusty tool Na2CO3 (aq) Iron sheet

3 [Turn over (iv) A consumer saw the DIY kit and decided to purchase it and try out on his rusted dumbbell. He prepared the set up as shown in Figure 1.1 with a 20 A power source and switched it on for 6 hours. Determine the change in mass of the iron sheet. [2] Q = It = 20 x 6 x 60 x 60 = 432000 C Amount of electrons = 432000 / 96500 =