Food cans are coated with tin and not with zinc because:

Food cans are usually made of steel (mostly iron), which rusts easily when exposed to moisture and air. To prevent this, the steel is coated with a thin layer of another metal. Steel coated with tin is called tinplate, and coating with tin is called tinning.

Tin is used for food cans because it is less reactive than zinc. In the reactivity series, the order is roughly: potassium > sodium > calcium > magnesium > aluminium > zinc > iron > tin > lead > hydrogen > copper > mercury > silver > gold. Zinc is quite reactive. It can react with the weak acids present in many foods, such as citric acid in fruits, acetic acid in pickles and lactic acid in other foods, and form zinc compounds that may be poisonous. Tin is much less reactive, so it does not react easily with food acids and is non-toxic in normal amounts. It also has a shiny, attractive appearance and is easy to apply. Today, the inside of many cans is also coated with a lacquer to keep the food from touching the metal.

Zinc coating is still widely used to protect iron in other places. Coating iron or steel with zinc is called galvanisation. It is used for buckets, roof sheets, pipes and fences. Galvanisation protects iron even if the coating is scratched, because zinc, being more reactive, corrodes first and protects the iron; this is called sacrificial protection. Tin protects iron only as long as the coating is unbroken; once scratched, the iron underneath may rust faster.

Other methods of preventing rust include painting, oiling, greasing, chrome plating and making alloys such as stainless steel.

Why not the other options?

• ✗Tin is more expensive than zinc, not cheaper.
• ✗Melting point is not the reason.
• ✗Good to know
• ✗Tin is less reactive than zinc, not more.