Question

1. (a) table 9.1 shows different types of alloys, their composition and uses. table 9.1 alloy composition use bronze copper and tin coins, medals solder lead and tin joining metals stainless steel iron, chromium, nickel and carbon kitchen utensils explain why 1 the use of alloys is recommended instead of pure metals, 2 bronze is used for making medals, 3 stainless steel is used for making kitchen utensils. 5 (b) (i) water from some sources form crust fur on the walls of the container. describe the source of the fur. 2 (ii) explain how the crust can be removed from the walls of the container. 1 (iii) suggest the effect of the crust on the time it takes for the water to boil. 1 (c) explain why rain water is a safe source of water for domestic use. 2 (d) describe how polyethene is produced from ethane. 4

Explanation:

1. Alloys are recommended over pure metals as they often have improved properties like higher strength, durability, and resistance to corrosion compared to pure metals.
2. Bronze is used for making medals because it has an attractive appearance, is relatively hard - wearing, and can be cast into detailed shapes.
3. Stainless steel is used for kitchen utensils as it is resistant to rust and staining, durable, and easy to clean due to its alloy composition.

(b)(i) The 'fur' is formed from dissolved calcium and magnesium compounds (hardness - causing substances) in the water that precipitate out as the water evaporates or heats up.
(b)(ii) The crust can be removed by using an acidic solution like vinegar which reacts with the calcium and magnesium compounds to dissolve them.
(b)(iii) The crust acts as an insulator, so it will increase the time it takes for the water to boil.
(c) Rain water is a safe source of water for domestic use as it is relatively pure when it falls, having been distilled during the water - cycle and contains few dissolved impurities or contaminants initially.
(d) Polyethene is produced from ethene through a polymerization reaction. Ethene monomers undergo addition polymerization where the double bond in ethene breaks, and the monomers link together to form long - chain polyethene molecules.

Answer:

1. Alloys have better properties like strength and corrosion resistance.
2. It has an attractive look, is durable and can be cast well.
3. It is rust - resistant, durable and easy to clean.

(b)(i) Dissolved calcium and magnesium compounds in water.
(b)(ii) Use an acidic solution like vinegar.
(b)(iii) Increases the boiling time.
(c) It is relatively pure with few dissolved impurities initially.
(d) Ethene monomers undergo addition polymerization to form long - chain polyethene molecules.