2024 Prelims NJC H2 Chem P3 (QP)

1 NJC/H2 Chem Preliminary Examination/03/2024 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/03 17 September 2024 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 /20 2 /20 3 /20 Section B (*circle the question you attempted) 4 /20 5 /20 Paper 3 Total /80 This document consists of 32 printed pages.

2 NJC/H2 Chem Preliminary Examination/03/2024 Section A Answer all the questions in this section. 1 (a) Chlorinated phenols have seen growing applications as fungicides, herbicides, insecticides, and as starting materials in the production of various pesticides since the 1930s. It can be readily produced from compound A using chlorine in water. compound A (i) Write a balanced equation for the reaction between compound A and excess aqueous chlorine. [1] (ii) Compound A undergoes a series of reactions shown in the reaction scheme below. State the reagent and condition for Reaction I and II, and hence draw the structures of B and E. [4] (iii) Write a balanced equation for reaction III. [1] ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..………………

3 NJC/H2 Chem Preliminary Examination/03/2024 [Turn over ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..……………… ………………………………………………………………………………..………………

4 NJC/H2 Chem Preliminary Examination/03/2024 (b) Vanadium is a transition element that exhibits variable oxidation states. (i) Explain why vanadium can form stable ions with varying oxidation states. [1] (ii) Write the full electronic configuration for V3+ . [1] (iii) Draw a fully labelled diagram of the experimental set -up used to measure the standard electrode potential of the VO2+ (aq)/V3+(aq) half-cell. [3] A Latimer diagram below summarises the standard electrode potential data of vanadium complexes in acidic medium. The standard electrode potential x for converting VO 3− to V 3+, is not the sum of +1.00 V and +0.34 V. Instead, it can be calculated from Gꝋ. (iv) Write the half-equation for the conversion of VO3− to V3+. [1] (v) Calculate the standard electrode potential x, given that Gꝋ for the conversion of VO3− to V3+ is −129 kJ mol-1. [1] …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… VO3− VO2+ V3+ +0.34 V +1.00 V x

5 NJC/H2 Chem Preliminary Examination/03/2024 [Turn over …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..…………………………………………………………………………………………… …..……………………………………………………………………………………………

6 NJC/H2 Chem Preliminary Examination/03/2024 (c) A vanadium redox battery is employed to store electrical energy produced at a wind farm in Tasmania. The diagram below illustrates the configuration of a cell in a vanadium redox battery. The reactants are dissolved in an acidic solution, stored in large tanks, and circulated through the cell. A polymer membrane facilitates the movement of specific ions. When discharging, the battery supplies electricity to the power grid on demand through a control switch. During charging, the battery uses electricity from the wind turbines to reverse the chemical reaction. (i) State the polarity of electrode A when the cell is discharging. Explain your answer. [2] (ii) Write an equation for the reaction that occurs when the cell is being charged. [1] …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..……………………………………………

7 NJC/H2 Chem Preliminary Examination/03/2024 [Turn over …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… …………………………………………………..…………………………………………… (d) The exhaust from heavy-duty diesel