2019 NJC 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 the Question Paper. Additional Materials: Data Booklet 9729/02 Monday 16 September 2019 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. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /17 2 /9 3 /17 4 /18 5 /14 P2 Total /75 Marks Weightings Paper 1 /30 15 % Paper 2 /75 30 % Overall Percentage Paper 3 /80 35 % Paper 4 /55 20 % Grade This document consists of 20 printed pages.

NJC/H2 Chem Prelim/02/2019 2 For Examiner’s Use 1 (a) Brass is a mixture of copper and zinc. When a piece of brass is placed in dilute hydrochloric acid, only one of the metals present dissolves. Explain the observation and write an equation for the reaction that occurs. ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………… ………………...…………………………………………………………………….……………[3] (b) Copper and zinc are the two electrodes in a Daniell cell. The cell is set up as shown in Fig 1.1. Fig 1.1 (i) Indicate the direction of electron flow on Fig 1.1. [1] (ii) Write the equation for the reaction taking place and calculate ΔGo for the reaction. ………………...…………………………………………………………………….…… [3]

NJC/H2 Chem Prelim/02/2019 3 For Examiner’s Use [Turn over (iii) Discuss the effect of the following changes on the cell potential of the above cell. (I) adding excess amount of aqueous ammonia into the Zn2+/Zn half-cell ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….…… [2] (II) using a smaller copper electrode ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….……….. ………………...…………………………………………………………………….…… [2] (iv) How many hours will it take for t his galvanic cell to plate 15.0 g of metallic copper from 1 mol dm–3 solutions of Cu2+(aq) and Zn2+