Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A galvanised bucket is an iron bucket with a zinc coat. A tin can is an iron can with a tin coat. Use , and . Explain what happens to the iron when each coat is scratched.
A reaction can happen if is positive. A metal with releases hydrogen from dilute acid. , with .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The galvanised bucket. Zinc has the lower than iron. When the coat is scratched, water touches both metals. Zinc is oxidised in preference to iron, so the iron stays unharmed until the zinc is used up.
Step 2. The tin can. Tin has the higher than iron. Where the coat is scratched, iron is now the easier metal to oxidise, and it rusts, faster than if there were no tin at all.
Answer: zinc protects iron even when scratched, because it is oxidised first. Tin protects iron only while the coat is unbroken, and then makes rusting worse.
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