2020 SAJC H2 Prelim Paper 3 (QP)

1 [Turn over ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CLASS 1 9 S CHEMISTRY Paper 3 Free Response Candidate answer on the Question Paper. Additional Materials: Data Booklet 9729/03 16 September 2020 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use a HB 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. 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 the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. This document consists of 37 printed pages. For Examiner’s Use Q1 19 Q2 19 Q3 22 Q4/5 20 Total 80

2 [Turn over Section A Answer all the questions in this section. 1 Elements in Group 17 are known as halogens. The term “halogen” means “salt-former” in Greek because these elements will readily react with alkali metal and alkaline earth metals to form important halide salts such as sodium chloride. (a) Describe and explain how the volatilities of the halogens vary down Group 17. [2] ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….

3 [Turn over (b) The table below shows the results of experiments in which the halogens, X2, Y2 and Z2 were added to separate aqueous solutions containing X–, Y– and Z– ions. The possible identities of the halogens are chlorine, bromine and iodine. X– (aq) Y– (aq) Z– (aq) X2 - no reaction Z2 formed Y2 X2 formed - Z2 formed Z2 no reaction no reaction - (i) Based on the results in the given table, identify X2, Y2 and Z2. Explain your answer. [1] (ii) Describe and explain how the solubility of the solid silver halides, Ag Cl, AgBr and AgI, is affected by adding concentrated NH3. [3] ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….

4 [Turn over (c) A student was presented the following set-up, which involved sodium chloride solution in one half-cell. The student predicted the following:  Hydrogen is produced at the cathode of cell 1 when concentrated or dilute sodium chloride solution is used.  The anode of cell 2 would increase in mass. (i) State which electrode, a to d, is the cathode of cell 1 and which is the anode of cell 2. [1] (ii) Do you agree with each of his prediction? Explain your answer. You should use relevant Eo values from the Data Booklet for cell 1. [3] ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. a b c d NaCl(aq) cell 1 cell 2

5 [Turn over ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. (d) Organohalogens are organic compounds that contain halogen atoms. The following compounds are examples of organohalogens. (i) Suggest and explain how the acidity of compound A might compare with that of compound B. [2] (ii) Describe and explain the relative reactivity of compounds A and C with respect to hydrolysis. [2] (iii) Suggest a simple chemical test to distinguish compounds B and C. State the observation and write equation(s) to explain the reactions that happened. [3] ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….

6 [Turn over ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….

7 [Turn over Jones oxidation can be used to oxidise compound A to compound B. Jones reagent uses chromium trioxide dissolved in sulfuric acid, to form chromic (VI) acid, HCrO4−. During the reaction, HCrO4− is reduced to Cr3+. (iv) Determine the change in oxidation number for the carbon atom that is directly bonded to oxygen atom in compounds A and B. [1] (v) Hence, using oxidation numbers, construct a balanced equation for this reaction. You should use RCH2OH and RCO2H to represent compounds A and B respectively. [1] ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. [Total: 19]

8 [Turn over 2 Ozone, O3, is a powerful oxidising agent that can destroy viruses and bacteria. Ozone is used to disinfect water and sterilise food. (a) To generate ozone for industrial use, electricity is passed briefly through oxygen gas. Some oxygen molecules decompose to form oxygen atoms, which collide with more oxygen gas to form ozone, until an equilibrium is reached. 3O2 (g) ⇌ 2O3 (g) (i) Draw a dot -and-cross diagram to show the bonding present within an ozone molecule and suggest a value for its bond angle. [2] (ii) Write an expression for Kp for this equilibrium. [1] (iii) The value of Kp under a particular set of industrial conditions is 5 x 10–8. Deduce the sign and magnitude for ΔG at these conditions. [2] (iv) Predict and explain the effect of compressing the volume of the reaction mixture on the yield of ozone. [2] ………………………………………