An outdoor sculpture is made from painted steel, which contains iron. A scratch allows oxygen and water to reach the steel. A copper block is attached to try to give sacrificial protection.
Why will the copper block fail to protect the scratched steel?
Copper forms positive ions more readily than iron, so the copper corrodes away before it can protect the iron.
Sacrificial protection works only under unbroken paint, so it cannot protect iron exposed by a scratch.
Iron forms positive ions more readily than copper, so the exposed iron corrodes instead of the copper.
Copper and iron are both below carbon in the reactivity series, so neither metal can protect the other.
136 exam-style questions on OCR GCSE Chemistry 6.1 Improving processes and products, covering 6.1.1 Extracting metals industrially and by electrolysis, 6.1.2 Life cycle assessment and recycling, 6.1.3 Biological methods of metal extraction, 6.1.4 The Haber process and the production of fertilisers, 6.1.5 Alloys and their uses, 6.1.6 Corrosion and its prevention, 6.1.7 Comparing and selecting materials, and 6.1.8 Industrial conditions, rate and position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.