CGSS 2023 Chemistry Paper 2B

CEDAR GIRLS’ SECONDARY SCHOOL Preliminary Examination 2023 Secondary Four CANDIDATE NAME CLASS 4 INDEX NUMBER CHEMISTRY 6092/2 Paper 2 Section B 29 August 2023 1 hour 45 minutes Additional Materials: NIL For Examiner’s Use Section B 7 12 8 8 9 EITHER 10 9 OR 10 Total 30 [Turn over

14 Section B Answer all three questions in this section. The last question is in the form of an either/or and only one of the alternatives should be attempted. B7 The chemistry of ceramic pottery Ceramic objects are made by combining naturally occurring raw materials such as clay and water and shaping them into different forms. Once shaped, the object is fired and glazed. Clay Clay is made up on aluminium silicates with alkali metals. One such example is orthosclase, whose composition is shown in Table 7.1. Table 7.1 component in orthosclase percentage composition / % potassium oxide 16.9 aluminium oxide 18.3 silicon dioxide 64.8 Forming a pot Clay is easily shaped because the layers of clay are separated by a thin layer of water molecules which are linked to neighbouring layers via intermolecular forces of attraction. These weak but useful forces enable different types of pottery vessels to be formed. Fig. 7.1 shows the simplified structure of clay. Fig. 7.1

15 [Turn over Firing the pot Table 7.2 gives information for each stage of the firing process in the kiln, an oven that produces high temperatures, to obtain ceramic. Table 7.2 Stage Temperature range / oC Information 1 Below 100 The kiln is set to a temperature below the boiling point of water and it is held at that temperature for a few hours. The water that evaporates out of the clay readily is called ‘free water’. 2 480 – 700 The water that is left after Stage 1 is called ‘chemical water’. Driving off the ‘chemical water’ leads to the formation of new covalent bonds. This is shown in the simplified equation: [clay]−OH + HO−[clay] → [clay]−O−[clay] + H2O 3 1100 – 1200 Non-metal compounds in clay is oxidised . Sulfur containing compounds burn in air to create a gas which irritate the eyes upon contact. 4 Quartz in the clay melts and hardens to form glass between particles in the clay. This process makes the clay less porous. 5 − Ceramic pieces are left to cool down slowly. Glazing the pot The pot is then glazed for functional and decorative reasons. The main minerals (silicon dioxide and aluminium oxide) comprising glazes are colourless. However, glazes made from the oxides of transition metals are used to improve the appearance.

16 For Examiner's Use (a) Which compound in orthosclase shows that it comprises of alkali metals? ……………………………………………………………………………..…….…… [1] (b) Explain why the intermolecular forces of attraction between layers of clay are considered weak but useful in shaping clay. ……………………………………………………………………………..….……… ……………………………………………………………………………..….……… ………………………………………………………………….…………..………… ……………………………………………………………………………..……….… [2] (c) If Stage 1 is conducted above the boiling point of water, the clay object will explode. Explain why this happens using ideas of Kinetic Particle Theory. ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… [2] (d) Explain, in terms of bonding, the difference in the temperature required for the removal of chemical water in Stage 2 compared to free water in Stage 1. ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… [2] (e) Suggest the identity of the gas produced in Stage 3 and explain why it irritates the eyes upon contact. ……………………………………………………………………………..……….… ……………………………………………………………………………..……….… [2]

17 [Turn over For Examiner's Use (f) Describe and explain how the melting of quartz makes the pot less porous in Stage 4. Your answer should include: • the change in movement of particles as quartz melts • how this change in movement makes the pot less porous ……………………………………………………………………………..………… ……………………………………………………………………………..………… ……………………………………………………………………………..………… ……………………………………………………………………………..………… ……………………………………………………………………………..………… [2] (g) State a property of the oxides of transition metals that enables it to be used for decorative reasons. ……………………………………………………………………………..………… [1] [Total:12]

18 For Examiner's Use B8 A student, Joan wanted to investigate the rate of rusting of iron nails under different conditions. She set up the experiment as shown. After 48 hours, she observed that the iron nail in beaker 1 turned slightly rusty but the iron nail in beaker 2 remained unchanged. (a) Chemical analysis of the rust formed on the iron nail shows that the rust is hydrated iron(III) oxide with the formula Fe2O3•nH2O. The ‘n’ in the chemical formula of rust indicates the number of water molecules present in the compound. With the aid of a balanced chemical equation and the information provided, describe the process of rusting of the iron nail. ………………………………………………..……………………………………… …………………………………………………..…………………………………… ……………………………………………………………………………………….. [2] (b) Joan set up two other beakers, 3 and 4 with iron nail s under similar experimental conditions, in which the iron nail is connected to metal strip X and Y respectively via a wire. After 48 hours, Joan observed that for beaker 3, the iron nail remained unchanged, whereas for beaker 4, almost the entire iron nail turned rusty. (i) Based on Joan’s experiment, arrange the three metals (Fe, X and Y) in increasing order of reactivity. ………………………………………………………………………………… [1]

19 [Turn over For Examiner's Use (ii) Explain the order of reactivity as stated in b(i). ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (iii) Hence, suggest an identity for metal X. ………………………………………………………………………………… [1] (c) Iron is usually further processed to make steel, which is stronger. Use ideas about the arrangement of atoms in steel to explain why. You may use a labelled diagram to support your answer. ………………………………………………………………………..……………… ………………………………………………………………………..……………… ……………………………………………………………………………….….…… ……………………………………………………………………………….………. [2] [Total: 8]

20 For Examiner's Use EITHER B9 This question is about esters. Ester A reacts with water to form ethanoic acid and ethanol. The displayed formulae of the reactants and products are shown in this equation: The enthalpy change (H) for the reaction is 0 kJ mol-1. (a) (i) Give the name of ester A. ………………………………………………………………………………… [1] (ii) Describe a chemical test, other than using an indicator, to confirm that the reaction mixture contains ethanoic acid. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (iii) Explain why the enthalpy change (H) for the reaction between ester A and water is 0 kJ mol-1. State the bonds broken and formed in your answer. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (iv) State the type of reaction and the chemicals needed for the conversion of ethanol to ethanoic acid in the laboratory