ASRJC 2021 J2Prelims H2Chem P2 QP

ASRJC JC2 PRELIMS 2021 9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2021 JC 2 PRELIMINARY EXAMINATION NAME:_________________________________ ( ) CLASS: 21 /____ CHEMISTRY 9729/02 Paper 2 Structured Questions 14 September 2021 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces at the top of this page. 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 2 1 /21 2 /10 3 /13 4 /10 5 /11 6 /10 Total /75 This document consists of 23 printed pages and 1 blank page.

2 ASRJC JC2 PRELIMS 2021 9729/02/H2 Answer all the questions in the spaces provided. 1 (a) Describe and explain the trend in electronegativity of elements across Period 3 from sodium to chlorine. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. ……………………………………………………………………………………………………….[2] (b) Some ionic radii are listed in the Data Booklet. (i) Explain the trend in ionic radius down Group 2. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………[2] (ii) Explain the differences between the ionic radii of P3–, Cl– and Ca2+. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………[1] (iii) Hence, suggest a value for the ionic radius of a potassium ion, K+. …………………………………………………………………………………………………[1]

3 ASRJC JC2 PRELIMS 2021 9729/02/H2 [Turn over (iv) Explain the difference in size between the radius of the potassium ion and the radius of a potassium atom. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………[1] (c) Anodisation of aluminium is a process which coats an oxide layer on aluminium objects. (i) Draw a labelled diagram of the electrolysis cell used to anodise a small piece of aluminium object. Include details of the cathode, anode and electrolyte. [1] (ii) Complete Table 1.1 to show the type of reaction occurring, with the relevant half–equations, during the anodisation of the aluminium object. Table 1.1 type of reaction occurring half–equation(s) anode cathode [2]

4 ASRJC JC2 PRELIMS 2021 9729/02/H2 (d) The molecules of alcohol P, C7H16O, are optically active and does not react with hot, acidified Na2Cr2O7(aq). On treatment with Al2O3, P produces a mixture of four different isomeric alkenes with the formula C7H14, only two of which are cis–trans isomers of each other. Suggest the structural formula of compound P and the four alkenes. [4]

5 ASRJC JC2 PRELIMS 2021 9729/02/H2 [Turn over Question 1 continues on the next page.

6 ASRJC JC2 PRELIMS 2021 9729/02/H2 (e) The following equilibrium exists in a sample of aluminium chloride vapour. Al2Cl6(g) ⇌ 2AlCl3(g) (i) Draw a dot–and–cross diagram of the Al2Cl6 molecule, including its co–ordinate bonds. [1] When 1.50 g of aluminium chloride was introduced into an evacuated flask of 250 cm3 capacity and heated to 500 K, the pressure inside the flask rose to 1.16 x 105 Pa. (ii) Assuming the gaseous mixture behaves ideally, calculate the average Mr of the mixture. Give your answer to four significant figures. [2] (iii) Using the following relationships, calculate the mole fraction of Al2Cl6, x and the mole fraction of AlCl3, y, in the mixture. x + y = 1 average Mr = 267x + 133.5y [1]

7 ASRJC JC2 PRELIMS 2021 9729/02/H2 [Turn over (iv) Hence calculate the partial pressures of Al2Cl6 and AlCl3 in this mixture. [1] (v) Write an expression for Kp for the reaction, and calculate its value. Include units in your answer. [2] [Total: 21]

8 ASRJC JC2 PRELIMS 2021 9729/02/H2 2 (a) When Group 2 iodates(V), M(IO3)2, is heated, it behaves in a similar way to the Group 2 carbonates. Upon heating, it decomposes as shown. 2M(IO3)2(s) ® 2MO(s) + 2I2(g) + 5O2(g) (where M is a Group 2 metal) (i) Using your knowledge of Group 2 carbonates, suggest and explain the trend in thermal stabilities of the Group 2 iodate(V). ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …...…………………………………………………………………………………………….[2] X, Y and Z are Group 2 metals (Mg to Ba, not necessarily in that order). X(IO3)2, Y(IO3)2 and Z(IO3)2 are Group 2 iodates(V). The three graphs in Fig. 2.1 show the change in mass when 2.00 g each of X(IO3)2, Y(IO3)2 and Z(IO3)2 were heated separately at a temperature T oC. Fig. 2.1 (ii) With reference to the information from Fig. 2.1, show, by calculations, that none of the above iodate(V) samples contains Mg(IO3)2. [2]

9 ASRJC JC2 PRELIMS 2021 9729/02/H2 [Turn over (iii) Hence, suggest the identities of the three iodates(V). [No calculation is required.] iodates(V) X(IO3)2 Y(IO3)2 Z(IO3)2 identity [1] (b) When a salt such as a Group 2 sulfate dissolves in water, the lattice energy must be overcome. (i) How will the magnitude of the lattice energy of Group 2 sulfates change from MgSO4 to BaSO4? ………………………………………………………………………………………………….... ………………………………………………………………………………………………....[1] (ii) Suggest a reason for this trend. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………....…[1] (iii) Draw a simple diagram to show how a water molecule can be attached to a magnesium cation, and to a sulfate anion. Show the displayed structure of the sulfate anion in your answer and label each diagram to show the type of interaction involved. Mg2+ cation SO42– anion [3] [Total: 10]

10 ASRJC JC2 PRELIMS 2021 9729/02/H2 Question 3 starts on the next page.