2025 H2 Chem Prelim P3 Answers_VJC

© VJC 2025 9729/03/PRELIM/2025 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ANSWERS ……………………………………………….………….. …………………………….. CHEMISTRY 9729/03 Paper 3 Free Response 17 September 2025 2 hours Additional Materials: Data Booklet ________________________________________________________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name and CT group on this cover page. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 20 2 / 20 3 / 20 4 / 20 5 / 20 Total / 80 This document consists of 23 printed pages and 1 blank page.

2 © VJC 2025 9729/03/PRELIM/2025 Declocalised electrons Metal cations Section A Answer all the questions in this section. 1 (a) Potassium is a highly reactive alkali metal that must be stored under oil, while copper is a much less reactive metal that resists corrosion. Table 1.1 shows the melting points of both metals. Table 1.1 metal Melting point / C K 63.5 Cu 1085 (i) Copper does not react with most dilute acids, unlike potassium. With reference to the standard electrode potentials in the Data Booklet, explain why this is so. [2] Cu2+ + 2e– ⇌ Cu +0.34 V K+ + e– ⇌ K –2.92 V 2H+ + 2e ⇌ H2 0.00V Or Eo (Cu2+|Cu) = +0.34 V Eo (K+|K) = -2.92 V Eo (H+|H2) = 0.00 V Copper is unable to react with dilute acids. For copper, Eocell = (0– 0.34)= –0.34V <0 (not spontaneous) Potassium can react with acid to produce H2 gas. For potassium, Eocell = (0– (–2.92))= 2.92V > 0 (spontaneous) • • Quote & calculation of EƟcell Explanation (ii) Describe with the aid of a labelled diagram the structure of copper at room temperature. [2] • • Copper has a giant metallic structure which is a three-dimensional arrangement of positive copper ions surrounded by delocalised electrons , held together by strong electrostatic forces of attraction. (iii) Suggest why the melting point of copper is significantly higher than that of potassium as shown in Table 1.1. [2] • Potassium can only delocalise its single 4s electron while