ACJC 2022 Prelim P2 QP

3 © ACJC 2022 9729/02/Prelim/2022 [Turn over Answer all the questions in the spaces provided. 1 (a) Table 1.1 shows the solubility of two organic molecules at 25 °C. Table 1.1 solubility in water / g dm–3 propanone miscible chloromethane 5.04 (i) Identify the type of intermolecular force present between the molecules. propanone: …………………………………………………………………........ chloromethane: ……………………………………………………………….[1] (ii) Give a reason for the difference in their solubilities in water. ………………………………………………………………………………...….. ………………………………………………………………………………….[1] (b) The boiling point of three ligands are shown in Table 1.2. Table 1.2 ligand formula boiling point / °C water H2O 100 ammonia NH3 –33.3 hydrazine N2H4 114 (i) Explain what is meant by the term ligand. ………………………………………………………………………………...….. ………………………………………………………………………………….[1] (ii) Explain the difference in the boiling points of the three ligands. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………….[2]

4 © ACJC 2022 9729/02/Prelim/2022 [Turn over (c) Polydentate ligands are ligands which form more than one bond with the metal atom or ion. Salicylaldehyde, ethane-1,2-diamine and H2salen are examples of such ligands. H2salen can be synthesised from salicylaldehyde and ethane-1,2-diamine. When the phenolic groups of H 2salen are deprotonated, salen 2– acts as a ligand. It has a high affinity for Co2+ ions and forms a planar complex Co(salen). (i) Suggest the identity of molecule X. ………………………………………………………………………………….[1] (ii) Draw the structure of a salen2– ligand and circle the atoms which are used to coordinate to a Co2+ ion. salen2– [2] (iii) State the coordination number of the Co2+ ion in Co(salen). ………………………………………………………………………………….[1] (d) Ozonolysis is a method to oxidatively cleave alkenes using ozone, O3, to form carbonyl compounds.

5 © ACJC 2022 9729/02/Prelim/2022 [Turn over (i) 2-methyl-3-ethylpent-2-ene Draw the structure of the organic products when 2-methyl-3-ethylpent-2-ene undergoes ozonolysis. [2] (ii) Ozonolysis of A,C6H10, gives a single compound, B,C6H10O2. B gives a yellow precipitate when treated with alkaline aqueous iodine and forms a red-brown precipitate when treated with Fehling’s solution. Draw the structures of the compounds A and B. [2] [Total: 13] AA A B

6 © ACJC 2022 9729/02/Prelim/2022 [Turn over 2 Chromium is a transition metal that is valued for its high resistance to corrosion and is added to steel to form stainless steel. While chromium can exist in various oxidation states, the most common oxidation state is the +3 state. (a) Hydrated chromium (III) chloride exists as isomers, with the general formula of CrCl3.6H2O. One such isomer is [CrCl2(H2O)4]Cl.2H2O and it appears dark green. Suggest the formula of two other isomers of hydrated chromium (III) chloride. isomer 1 ………………………………………………………………...…………….. isomer 2 …………………………………………………………………………….[2] (b) When a sample of hydrated chromium (III) chloride is added to excess water, a green solution of CrC l3(aq) is obtained. Fig. 2.1 shows the reactions that aqueous CrCl3 can undergo. Fig. 2.1 (i) Identify precipitate A and gas B. precipitate A: ………………………………………………………………...… gas B: ………………………………………………………………………….[2] (ii) Suggest the formula of compound C. ………………………………………………………………………………….[1] CrCl3(aq) green solution Na2CO3(aq) grey-green precipitate A + effervescence of gas B C dark green solution D violet solution excess NaOH(aq) left to stand H2O2(aq), heat CrO42–(aq) yellow solution

7 © ACJC 2022 9729/02/Prelim/2022 [Turn over (iii) Explain why solutions of transition metal compounds are often coloured. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ……………………………………………………………………………….... [3] (iv) Given that the oxidation state of chromium in compound D is still +3, suggest what happened that caused the colour change from green to violet. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ……………………………………………………………………………….…[2] (v) State the role of H2O2(aq). ……………………………………………………………………………….…[1] (vi) Write a balanced equation for the formation of CrO42– from C. ……………………………………………………………………………….…[1]

8 © ACJC 2022 9729/02/Prelim/2022 [Turn over (c) Fig. 2.2 shows the first seven ionisation energies of calcium and chromium. Fig. 2.2 State and explain w hich graph shows the successive ionisation energies f or calcium. ………………………………………………………………………………...………… ………………………………………………………………………………...………… ………………………………………………………………………………...………… ………………………………………………………………………………...………… ………………………………………………………………………………...………… ………………………………………………………………………………...………… ……………………………………………………………………………….………. [2] [Total: 14]

9 © ACJC 2022 9729/02/Prelim/2022 [Turn over 3 (a) The variation of the volume with temperature of a fixed mass of an ideal gas at constant pressure may be represented by a relationship known as Charles’s law, V = k T where V is the volume of a gas, T is the temperature in Kelvin and k is a constant. An experiment was carried out to attempt to verify this law using a gas, phosphine, PH3. The experiment was repeated several times at different temperatures. Fig. 3.1 was plotted to determine the relationship between the volume of the gas and its temperature. Fig. 3.1 temperature of the gas/ K volume of the gas/ cm3 0 10 20 0 30 0 40 10.0 20.0 30.0 40.0

10 © ACJC 2022 9729/02/Prelim/2022 [Turn over (i) Based on Fig. 3.1, state whether the result is consistent with Charles’s law. Give a reason for your answer. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………….[1] (ii) State the two properties of a gas necessary for it to approach ideal behaviour. ………………………………………………………………………………...….. …………………………………………………………………………..……...… ……………………………………………………………………….…………… ………………………………………………………………………..………...… ………………………………………………………………………………….[1] (b) Orange street lamps contain sodium with a small amount of neon. The light is produced when gaseous atoms are ionised in an electric field. When it is first turned on, the lamps emit a red glow characteristic of neon, but after some time, the orange glow of sodium predominates. Explain the order for the