VJC 2022 H2 Chem Prelim P2 qp

1 © VJC 2022 9729/02/PRELIM/22 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/02 Paper 2 Structured Questions Candidates answer on the Question Paper. 15 September 2022 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group in the space at the top of this page. 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 space 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 / 25 2 / 13 3 / 12 4 / 19 5 / 6 Total / 75 This document consists of 18 printed pages.

2 © VJC 2022 9729/02/PRELIM/22 [Turn over 1 (a) The most common oxidation states of iron are +2 and +3. (i) Iron(II) and iron(III) both contain electrons in all five 3d orbitals. Sketch and label the shape of the following two 3d orbitals: • one 3d orbital from the lower energy level in an octahedral complex • one 3d orbital from the higher energy level in an octahedral complex Use the axes below. (ii) Explain why Fe2+(aq) ions are coloured, whereas Zn2+(aq) ions are colourless. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [3] (iii) Most naturally occurring samples of iron( II) oxide are found as the mineral w üstite. Wüstite has formula Fe20Ox. It contains both Fe2+ and Fe3+ ions. 90% of the iron is present as Fe2+ and 10% is present as Fe3+. Deduce the value of x. [1] lower energy level higher energy level z y x

3 © VJC 2022 9729/02/PRELIM/22 [Turn over When aqueous solutions of S 2O82– and tartrate ions, C 4H4O62–, are mixed, the reaction proceeds very slowly. However, this reaction proceeds quickly in the presence of an Fe3+(aq) catalyst. The overall equation for this reaction is as shown. C4H4O62– + 3S2O82– + 2H2O → 2CO2 + 2HCO2– + 6H+ + 6SO42– (iv) State and explain the type of catalyst that Fe3+(aq) functions in the above reaction. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [1] (v) Write two equations to show how Fe3+(aq) functions as a catalyst in this reaction. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [2] (b) (i) Complete the ‘dot-and-cross’ diagram below, drawing the outer electrons only, to show the bonding in methanoic acid, HCO 2H. The two oxygen atoms in HCO 2H are labelled O1 and O2 respectively. [1] (ii) The carbon atom in HCO2H is sp2 hybridised. Explain what is meant by sp2 hybridisation with reference to the carbon atom in HCO2H. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [1] C O2 H H O1 • • x x

4 © VJC 2022 9729/02/PRELIM/22 [Turn over (iii) Similar to carbon, oxygen atom can also undergo hybridisation. By considering the number of electron densities around oxygen atom labelled O 1, suggest the type of hybridised orbitals for the oxygen atom labelled O1. ……………………………………………………………………………………………………... [1] (iv) Sketch a diagram to show how two sp2 hybridised orbitals can form a sigma bond. [1] (c) Cyclohexane is immiscible with water. Iodine, I2, can dissolve in both water and cyclohexane. The expression and numerical value for the partition coefficient, Kpc, of iodine between cyclohexane and water are given below. Kpc = concentration of I2 in cyclohexane concentration of I2 in water = 93.8 (i) 15.0 cm3 of C6H12 is shaken with 20.0 cm 3 of an aqueous solution containing I2 until no further change is seen. It is found that 0.390 g of I2 is extracted from water into the C6H12. Calculate the mass of I2 that remains in the aqueous layer. Show your working. [2]

5 © VJC 2022 9729/02/PRELIM/22 [Turn over (ii) Suggest how the value of Kpc of I2 between hexa-2-one, CH3(CH2)3COCH3, and water would compare to the value given in (c). Explain your answer. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [2] (d) Some data relating to calcium and oxygen are listed in Table 1.1. Table 1.1 process value / kJ mol–1 first ionisation energy of oxygen +1310 second ionisation energy of oxygen +3390 first electron affinity of oxygen –142 second electron affinity of oxygen +844 enthalpy change for 1 2O2(g) + 2e– → O2–(g) +951 enthalpy change for Ca(s) → Ca2+(g) + 2e– +1933 lattice energy of CaO(s) –3517 (i) Suggest why the first electron affinity of oxygen is negative. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [1] (ii) Suggest why the second electron affinity of oxygen is positive. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [1]

6 © VJC 2022 9729/02/PRELIM/22 [Turn over (iii) Oxygen exists as O 2 molecules. Use relevant data from table 1.1 to c alculate the bond energy of the O=O bond. Show your working. [2] (iv) Use relevant data from Table 1.1 to calculate the enthalpy change of formation of calcium oxide, CaO(s). Show your working. [2] (v) The lattice energy of lithium fluoride, LiF(s), is –1022 kJ mol–1. Identify the factor that causes the lattice energy of calcium oxide to be more exothermic than that of lithium fluoride. Explain why this factor causes the difference in lattice energies. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [2] [Total: 25]

7 © VJC 2022 9729/02/PRELIM/22 [Turn over 2 (a) Chlorine can be manufactured using the electrolysis of NaCl(aq). At the cathode, H2(g) and OH–(aq) are produced. At the anode, the product mixture contains both Cl2(g) and O2(g). The mole ratio of e