Preventing rusting by using sacrificial protection
3 marks · NormalRusting occurs when iron is exposed to air and water. Ships are often fitted with blocks of zinc on their hulls.
Explain, using the ideas of oxidation and reactivity, how these zinc blocks prevent the iron hull from rusting.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Zinc is more reactive than iron, so it oxidises (loses electrons) in preference to iron. The zinc corrodes, supplying electrons to the iron so the iron does not rust.
Also accept: Zinc acts as a sacrificial anode, being oxidised instead of iron, so iron remains protected and does not corrode.
Common mistakes: Not mentioning electron transfer or oxidation.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States zinc is more reactive than iron.
M2 (a) · 1 mark · States zinc oxidises/loses electrons in preference to iron.
A1 (a) · 1 mark · Explains that the zinc corrodes and iron is protected from rusting (by electrons from zinc or otherwise).
Worked solution
Zinc is more reactive than iron, so it is preferentially oxidised. It loses electrons and forms zinc ions. These electrons are supplied to the iron hull, preventing the iron from oxidising and rusting.