(a) (i) List the two gaseous fuels produced from coke. (ii) Which of the two fuels listed in 5(a)(i) is a better fuel? (iii) Give reasons for your answer in...

Answer Details

(a)(i) Water gas (CO + H₂) and producer gas (CO + N₂).

(a)(ii) Water gas is the better fuel.

(a)(iii) Water gas has a higher heating (calorific) value because it is a mixture of two combustible gases (CO and H₂) and is not diluted by large amounts of non-combustible nitrogen, whereas producer gas contains much inert N₂.

(a)(iv) Water gas: \[ \text{C} + \text{H}_2\text{O} \to \text{CO} + \text{H}_2 \] Producer gas: \[ 2\text{C} + \text{O}_2 \to 2\text{CO} \quad (\text{air over hot coke}) \]

(b)(i) Thermosets harden permanently once moulded and cannot be softened or re-shaped on further heating (they are cross-linked); thermoplastics soften on heating and can be re-moulded repeatedly.

(b)(ii) I. Thermoset: bakelite (or melamine). II. Thermoplastic: polythene (polyethene) (or PVC).

(b)(iii) Plastics are light, resistant to corrosion/chemicals, and poor conductors of heat and electricity (also easily moulded).

(c)(i) By downward delivery (upward displacement of air), collecting the gas in an upright jar.

(c)(ii) Ammonia and hydrogen chloride.

(c)(iii) They are extremely soluble in water, so the water rushes up to fill the partial vacuum created when the gas dissolves, producing the fountain.

(d)(i) Anhydrous copper(II) sulphate (white to blue) and anhydrous cobalt(II) chloride (blue to pink).

(d)(ii) Hard water wastes soap (forms scum), forms scale/fur in kettles, boilers and pipes, and the scale reduces heat efficiency and can block pipes.