2024 MI PU3 H2 Chem EOY P3 answers (final) w EC

Class Adm No Candidate Name: This question paper consists of 28 printed pages. 2024 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/03 Paper 3 Free Response 13th Sep 2024 2 hours Candidates answer on separate 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 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 19 23 18 20 80

2 Section A Answer all the questions in this section. 1 The halogens are elements in Group 17 of the Periodic Table . The name “halogen” translates to “salt producer”, due to their tendency to form salts readily in the presence of Group 1 metals such as sodium. (a) (i) Citing relevant data values, state and explain the trend of reactivity of the halogens as oxidising agents. [3] Electrode reaction Eo / V F2 + 2e– ⇌ 2F– +2.87 Cl2 + 2e– ⇌ 2Cl– +1.36 Br2 + 2e– ⇌ 2Br– +1.07 I2 + 2e– ⇌ 2I– +0.54 any 3, equation not required [1] Down Group 17, reactivity of the halogens decreases. [1] Down the group, Eo value becomes less positive and the halogens are less readily reduced. [1] Examiners’ Comments: - Many candidates can use the correct concept to explain. - Most common mistakes include the use bond energy to explain, not linking back to the question on reacti vity, and not giving at least 3 Eo values to state the trend. - (ii) Outline a procedure to demonstrate the relative reactivities of chlorine and bromine, given only the following reagents to choose from: Cl2(aq) Cl–(aq) Br2(aq) Br–(aq) [2] To a test tube containing 1 cm3 of Br–(aq), add 1 cm3 of Cl2(aq). [1] sufficient, but can also do the reaction between Cl– and Br2 The colourless solution will turn orange as the more reactive C l2 displaces Br – to produce Br2. [1] Examiners’ Comments: - Few candidates gave succinct procedure despite the question using “outline” as a command word. - A number of candidates also did not mention the initial colour of the solution for the observation.