2021 MI Prelim H2 Chemistry P3 (9729_03) Answers

Class Adm No Candidate Name: This question paper consists of 28 printed pages and 2 blank page. 2021 Preliminary Examinations Pre-University 3 H2 CHEMISTRY 9729/03 Paper 3 Free Response 17 Sep 2021 2 hours 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. Section A: Answer all questions Section B: Answer any 1 question A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. You are reminded of the need for good English and clear presentation in your answers. 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. Section A Section B Total Question 1 2 3 4 5 Marks 24 20 16 20 20 80

2 Section A Answer all questions from this section. 1 (a) A metallic element, M, exists as three isotopes. The relative isotopic masses and their relative abundances are shown in Table 1.1. Relative Isotopic Mass Relative Abundance 53.94 3 55.93 46 56.94 1 Table 1.1 (i) Define the term relative isotopic mass. [1] Relative isotopic mass is defined as the mass of one atom of an isotope compared to 112 of the mass of one atom of 12C. (ii) Using the information in Table 1.1, calculate the relative atomic mass of M, leaving your answer to 2 decimal places. [1] Relative atomic mass = ("#.%&×#))("".%#×&*))("*.%&×+)(#)&*)+)=55.83 A dilute aqueous solution of the chloride salt of M, MCln, was electrolysed using a current of 0.5 A for 1 hour as shown in the setup in Fig. 1.1. The experiment was carried out at 32 °C and 1 atm. Fig. 1.1 0.3471 g of metal M was deposited at electrode B.

3 [Turn over (iii) Using your answer in (a)(ii), determine n. [3] Amount of M deposited = ,.#&-+""..#=0.006217 𝑚𝑜𝑙; Q = 0.5 × 1 × 60 × 60 = 1800 C Amount of electrons = +.,,%*",,=0.01865 𝑚𝑜𝑙 ; Mn+ + ne- → M n = ,.,+.*",.,,*/+-=3 ; (iv) A gas is produced at electrode A. Write the ion-electron equation for the reaction taking place at electrode A. [1] 2H2O → O2 + 4H+ + 4e– (v) Calculate the volume of gas produced at electrode A. [2] Amount of O2 = 0.01865 ÷ 4 = 0.004663 mol ; V = 0123= ,.,,&**#×..#+×(#/)/-#)+,+#/"=1.166×104& 𝑚#=117 𝑐𝑚# ; (vi) Suggest why electrode