02 2024 CCKSS 4E Prelim CHEM P2

2 Section A Answer all questions. 1 Use the list of substances to answer the questions. Each option may be used once, more than once or not at all. ammonium chloride barium sulfate lead (II) fluoride potassium carbonate potassium iodide potassium manganate(VII) sodium chloride (a) Which substance reacts with methanoic acid to produce a gas? …………………………………………………………………………………………….. [1] (b) Which substance is used to test for an oxidising agent? …………………………………………………………………………………………….. [1] (c) Which substance, when warmed with aqueous sodium hydroxide, produces a gas that turns moist red litmus blue? …………………………………………………………………………………………….. [1] (d) Which substance reacts with aqueous chlorine to form a brown solution? …………………………………………………………………………………………….. [1] (e) Which substance produces a pale yellow vapour when electricity is passed through its molten state? …………………………………………………………………………………………….. [1] (f) Which two salts cannot be prepared by titration method? ……………………………………… and …...………………………………………….. [1] [Total: 6]

3 2024 / S4 / CHEM / PRELIM / P2 2 Crystals of a salt produced was found to have the following composition by mass: 31.5% K, 25.6% Cu and Cl. (a) Deduce the empirical formula of the salt crystal formed. Show your working. Empirical formula: ……………………………….. [3] (b) (i) The ion of an isotope of copper has the formula 𝐶𝑢!"!#$$. Complete the table with information about this ion. subatomic particles number of subatomic particles protons neutrons electrons [1] (ii) Describe a chemical reaction that can be carried out to identify 𝐶𝑢!"!#$$. Include relevant observations in your answer. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ……………………………………………………………………………………… [2] [Total: 6]

4 2024 / S4 / CHEM / PRELIM / P2 3 Calcium carbide, CaC2, is an ionic compound. This compound is commonly used in industries for the manufacture of fertilisers and in steelmaking. Calcium carbide and carbon monoxide is produced when quicklime, CaO, reacts with carbon at high temperature. (a) Explain, in terms of structure and bonding, why there is a need to carry out this reaction at a high temperature. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………….. [3] (b) Write a balanced chemical equation, with state symbols, for this reaction. …………………………………………………………………………………………….. [2] (c) Calculate the percentage purity of a sample of quicklime when 8 g of quicklime is reacted with carbon to produce 2400 cm3 of carbon monoxide at room temperature and pressure. percentage purity: ………………………………….% [3] [Total:8]

5 2024 / S4 / CHEM / PRELIM / P2 4 Barium hydroxide is placed in a beaker. Ammonium chloride is then added into the beaker and the mixture is stirred. The equation below shows the reaction between barium hydroxide and ammonium chloride. Ba(OH)2∙8H2O(s) + 2NH4Cl(s) à BaCl2∙2H2O(s) + 2NH3(g) + 8H2O(l) Fig. 4.1 shows what happens when the beaker is placed on a wooden block with a small pool of water. at the start after a few minutes Fig. 4.1 (a) Suggest an explanation for the observations seen after the beaker was placed on the wooden block for a few minutes. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………… [2] (b) Draw an energy profile diagram for the reaction. Your diagram should include: • the reactants and products of the reaction • the energy profile and activation energy, EA, for the reaction • the enthalpy change of reaction, ΔH . [3] [Total: 5] energy/ kJ progress of reaction ice water wooden block mixture of barium hydroxide and ammonium chloride

6 2024 / S4 / CHEM / PRELIM / P2 5 Magnesium chloride can be produced by reacting 1.0 g of magnesium oxide with dilute hydrochloric acid. MgO (s) + 2 HCl (aq) à MgCl2 (aq) + H2O (l) A pH probe data logger is used to measure the pH changes when magnesium oxide is slowly added to 25 cm3 of 0.1 mol/dm3 of dilute hydrochloric acid. Fig. 5.1 shows the results of the changes in pH. Fig. 5.1 (a) Calculate the maximum mass of magnesium chloride that can be obtained from this experiment. Give your answer to three significant figures. maximum mass: ………………………………….g [3] (b) Explain the shape of the different regions of the graph as magnesium oxide is slowly added till it is in excess. region A………………………………………………………………………………………… …………………………………………………………………………………………………… region B………………………………………………………………………………………… …………………………………………………………………………………………………… region C………………………………………………………………………………………… …………………………………………………………………………………………….. [4] [Total: 7] pH mass of magnesium oxide added A B C

7 2024 / S4 / CHEM / PRELIM / P2 6 Cars have catalytic converters fitted to reduce problems caused by some of the exhaust gases. The diagram shows some of the gases that enter and leave a catalytic converter. (a) (i) Describe how nitrogen monoxide and carbon monoxide are formed in the engine of a car. …………………………………………………………………………………………… …………………………………………………………………………………………… ……………………………………………………………………………………… [2] (ii) Identify a health problem caused by nitrogen monoxide and carbon monoxide respectively. nitrogen monoxide..……………………………………………………………………. …………………………………………………………………………………………… carbon monoxide..……………………………………………………………………… ……………………………………………………………………………………… [2] (b) When catalytic converters were first available, some advertisements claimed they ‘solved all car environmental problems’. Explain why this is not true. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………….. [2] [Total: 6]

8 2024 / S4 / CHEM / PRELIM / P2 7 Citric acid is a weak acid that is commonly used as a natural food flavouring and in cleaning metal parts. Fig. 7.1 shows the structure of citric acid. Fig. 7.1 (a) State the number of carboxylic acid functional groups in a citric acid molecule. ……………………………………………………………………………………………... [1] (b) Citric acid is effective in removing rust, hydrated iron(III) oxide, from steel parts and is often used in cleaning metal objects. (i) It was suggested that since citric acid is effective in removing rust, steel parts should be soaked in citric acid to reduce the hassle of cleaning regularly. Do you agree with the above suggestion? Why? …………………………………………………………………………………………….. ………………………………………………………………………………………. [1] (ii) The student says that citric acid removes rust faster than sulfuric acid. Do you agree with the above statement? Why? …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ………………………………………………………………………………………. [2]

9 2024 / S4 / CHEM / PRELIM / P2 (c) It is thought that as calcium citrate is insoluble in water, it can be prepared by reacting citric acid with calcium carbonate. The mixture is then filtered, and calcium citrate is obtained as the residue. Comment whether this experimental technique is appropriate to be used to obtain calcium citrate. Explain your answer. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………… [2] [Total: 6] 8 2.00 g samples of different metal carbonates are heated strongly using a bunsen burner until there is no further change in mass. Table 8.1 shows the mass of solid remaining after heating. Table 8.1 carbonate mass after heating/ g copper(II) carbonate 1.29