23MIPrelim Answers (H2 Chem Paper 3)

Class Adm No Candidate Name: This question paper consists of 25 printed pages and 1 blank page. 2023 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/03 Paper 3 Free Response 18 September 2023 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 in the spaces at the top of this page. 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 page at the end of this booklet. The question number must be clearly shown. Section A Answer all 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 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 A B Total 1 2 3 4 / 5 Marks 24 19 17 20 80

2 Section A Answer all the questions in this section. 1 Aluminium is the most abundant metal in the Earth's crust. It has a great affinity towards oxygen, forming a protective layer of oxide on the surface when exposed to air. (a) Aluminium is protected from corrosion by a protective oxide layer. The thickness of the aluminium oxide layer on the surface of aluminium can be increased by anodising the aluminium. H2SO4 is used as an electrolyte in the anodising of aluminium. (i) Draw a well-labelled diagram to illustrate the electrolysis set-up for the anodisation of aluminium. [2] (ii) Write chemical equations to show the reactions at the anode and cathode during anodising. Include the overall equation in your answer. [3] (iii) The aluminium piece to be anodised has a surface area of 29.2 cm2. Determine the current required to pass through the set -up for 1.8 hours to form a 0.2 mm-thick protective layer of Al2O3 on the aluminium piece. [Density of Al2O3 is 3.95 g cm−3] [4] (iv) Give one example of an anodised aluminium object, and explain the advantages of anodising it. [1] ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ……………