ACJC H2 Chem 2021 Paper 2 - Question Paper

Name Index Number Form Class Tutorial Class Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 9729/02 Higher 2 Paper 2 Structured Questions 25 August 2021 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS CAREFULLY Write your name, index number, form class, tutorial class and subject tutor’s name on all the work you hand in. Write in dark blue or black pen. You may use an 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. 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. For Examiner's Use Question no. Marks 1 / 15 2 / 15 3 / 12 4 / 5 5 / 19 6 / 9 Presentation of answers TOTAL / 75 This document consists of 25 printed pages and 1 blank page. 9729/02/Prelim/2021 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2021 Department of Chemistry [Turn over

2 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over BLANK PAGE

3 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over Answer all the questions in the spaces provided. 1 Hydrobromic acid, HBr, is one of the strongest mineral acids known and is even stronger than hydrochloric acid. Both the industrial and laboratory syntheses of HBr are well documented due to the usefulness of HBr in many chemical reactions. (a) The primary industrial preparation of HBr involves the platinum -catalysed reaction between hydrogen and bromine at temperatures between 450 K to 700 K. H2(g) + Br2(g) ⇌ 2HBr(g) The reaction was carried out in a 250 m3 vessel at 334 C. (i) Calculate the amount of HBr present at equilibrium, given that the equilibrium partial pressure of HBr is 2 atm. [1] (ii) At 334 C, the equilibrium constant, Kp, for the above reaction is 2.50. Write the expression for the equilibrium constant, Kp, for the above reaction. [1] (iii) At equilibrium, the number of hydrogen molecules is ten times that of bromine molecules. Calculate the amount of bromine present at equilibrium. [2]

4 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over (iv) Given that the equilibrium in (a) was established using hydrogen and bromine only, determine the mass of bromine (in kg) that was used. [2] (v) Predict, with explanation, the effect on the equilibrium position if the volume was decreased at constant temperature. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ……………………………………………………………………………….………………...[1] (b) The preparation of the acid, HBr, in the laboratory can be carried out by the reaction between bromine, sulfur dioxide and water only. The only by-product formed is also a strong acid. (i) Write the equation for the above laboratory preparation of HBr. ……………………………………………………………………………….………………...[1] (ii) When concentrated solutions of the two products formed in the above preparation react with each other, Br2 is regenerated. State and explain the type of reaction that HBr undergoes. ………………………………………………………………………………...…………………. ……………………………………………………………………………….………………...[2]

5 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over (c) Inter and intra molecular bondings respectively can explain the trends in the volatility and thermal stability of the hydrogen halides. (i) State and explain the trend in the volatility of hydrogen halides from HF to HI. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ……………………………………………………………………………….………………...[3] (ii) State and explain the trend in the relative thermal stabilities of hydrogen halides from HF to HI. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ……………………………………………………………………………….………………...[2] [Total: 15]

6 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over 2 This question is about nitrogen and its oxides. (a) (i) N3 is isoelectronic with F and Na+. Define the term isoelectronic. ……………………………………………………………………………….………………...[1] (ii) Sketch a graph of the successive ionisation energies of all the electrons of a nitrogen atom. [2] (iii) State and explain how the ionic radius of N3 compares to that of P3. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ………………………………………………………………………………...…………………. ……………………………………………………………………………….………………...[2]

7 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over (b) N2O3 is a pale blue solid at very low temperatures. As the temperature is raised, N 2O3 dissociates to form colourless nitrogen monoxide gas, NO and brown nitrogen dioxide gas, NO2. The interesting feature of this reaction is that both products are molecular radicals, each with an unpaired electron on the nitrogen atom. N2O3(s) ⇌ NO(g) + NO2(g) Draw the dot-and-cross diagram for N2O3, stating the shapes and bond angles about each N atom. [3]

8 © ACJC 2021 JC2 H2 Prelim 2021 [Turn over (c) NO is an air pollutant produced by cigarette smoke, automobile engines and power plants. It reacts with oxygen to form NO2(g). 2NO(g) + O2(g) ⇌ 2NO2(g) The kinetics of the reaction was studied and the following results were obtained. experiment initial concentrations / mol dm3 initial rate of formation of NO2 / mol dm3 s1 NO O2 1 0.001 0.001 7.0  106 2 0.001 0.002 1.4  105 3 0.002 0.003 8.4  105 Use this data to deduce the order of reaction with res pect to each of the reactants. Hence, write the rate equation for the reaction and calculate a value fo