NJC_2025_H2_Chemistry_Prelim_P2_QP

[Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/02 16 September 2025 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 on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /16 2 /14 3 /17 4 /16 5 /12 Paper 2 Total /75 Marks Weightings Paper 1 /30 15% Paper 2 /75 30% Overall Percentag e Paper 3 /80 35% Paper 4 /55 20% Grade This document consists of 19 printed pages.

2 NJC/H2 Chem Prelim/02/2025 Answer all the questions in the spaces provided. 1 925 silver, also known as sterling silver, is an alloy that is commonly used to make jewellery. It consists of 92.5% silver and 7.5% other metals, such as copper, by mass. Over time, the alloy can form a tarnish of Ag2S(s) when it reacts with hydrogen sulfide, as represented by the following equation. 2Ag(s) + H2S(g)  Ag2S(s) + H2(g) (a) (i) Write the full electronic configuration for copper. ………………………………………………………………………………………………... [1] (ii) State and explain the difference in atomic radii for silver and copper. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... [2] (b) The Ag 2S tarnish on sterling silver can be removed until only sterling silver remains. A student weighs a tarnished sterling silver sample both before and after removing the Ag2S and records the data in Table 1.1. Table 1.1 mass before tarnish removal /g 54.23 mass after tarnish removal /g 52.34 Assuming that only Ag2S(s) is removed, calculate the amount of silver atoms removed. [1]

3 NJC/H2 Chem Prelim/02/2025 [Turn over (c) (i) Suggest and explain the relative magnitudes of the lattice energy of the silver compounds, Ag2S, Ag2O and Ag2Se. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... [2] (ii) Using relevant data from the Data Booklet and Table 1.2, construct an energ