Preventing rusting by galvanising
2 marks · EasyA steel railing has a surface area of 400 cm² and is to be protected from rusting by covering it with a thin layer of zinc (galvanising). If 0.15 g of zinc is needed to cover 100 cm², calculate the minimum mass of zinc needed to fully galvanise the railing. Give your answer to 2 decimal places.
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0.60 g (±0.01)
Also accept: 0.60; 0.6
Common mistakes: Multiplying by 0.15 instead of multiplying by 4
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Marking points
M1 · 1 mark · Correctly uses the ratio to scale up the mass of zinc for 400 cm² (e.g., 0.15 × 4 or sets up equivalent proportion).
A1 · 1 mark · Arrives at the correct answer of 0.60 g with unit.
Worked solution
Mass needed for 100 cm² = 0.15 g. The total area to cover is 400 cm².
Final answer: 0.60 g