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 con