Preventing rusting by using sacrificial protection

3 marks · Normal

A ship’s iron hull is protected from rusting by sacrificial anodes. Each anode is made from magnesium and has a mass of 6 kg. Over a year, each anode loses 1.5 kg of magnesium.

(a)

State one structure, apart from a ship, that is protected by sacrificial anodes.

[1 mark]

(b)

Calculate the percentage of magnesium lost from each anode in a year.

[2 marks]

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(a) Underground pipeline (or: oil rig, steel pier, water tank)

(b) 25%

Common mistakes: Dividing 1.5 by 12 months instead of total mass

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Marking points

B1 (a) · 1 mark · Correctly states any structure protected by sacrificial anodes (accept: pipelines, oil rigs, steel piers, water tanks).

M1 (b) · 1 mark · Correctly sets up the calculation: (mass lost / original mass) × 100.

A1 (b) · 1 mark · Arrives at correct percentage value (25%). Allow rounding ±1%.

Worked solution

a) An underground pipeline can be protected by sacrificial anodes.