Food cans are coated with tin and not with zinc because
20232024
Food cans are coated with tin and not with zinc because
Answer: C. zinc is more reactive than tin — Concept — the reactivity series ranks metals by how readily they give up electrons to acids, moisture and air. A metal used to line a container that holds…
- A.
zinc is costlier than tin
- B.
zinc has a higher melting point than tin
- C.
zinc is more reactive than tin
- D.
More than one of the above
- E.
None of the above
Show answer & explanation
Correct answer: C
Concept — the reactivity series ranks metals by how readily they give up electrons to acids, moisture and air. A metal used to line a container that holds food must be chemically inert towards the weak organic acids present in that food, because any metal that does react with them dissolves into the contents as soluble salts.
Application — zinc lies well above tin in the reactivity series. It is readily attacked by the citric, acetic and lactic acids found in canned food and passes soluble zinc salts into the food. Tin sits far lower in the series, below iron and only a little above hydrogen, and a thin adherent oxide film keeps it kinetically sluggish, so those same acids attack it only very slowly. A layer of electroplated tin a few micrometres thick therefore isolates the steel body of the can from its contents without contaminating them.
Cross-check — each offered comparison tested as a reason:
Comparison offered | Bearing on the choice of tin |
|---|---|
Cost | tin is the scarcer metal and trades at roughly an order of magnitude more per tonne than zinc, so cost would argue in favour of a zinc coating rather than against it. |
Melting point | zinc (about 419.5 °C) does melt higher than tin (about 231.9 °C), but a higher melting point is no disadvantage in a coating — it only changes how the coating is applied, by hot-dip galvanising for zinc and by electroplating or dipping for tin. |
Reactivity | the gap in reactivity is what settles the choice, because it decides whether the coating stays put or dissolves into the food. |
Contrast — zinc coatings are not inferior in general. Galvanised steel is standard for buckets, roofing sheets and water pipes, where the zinc corrodes sacrificially and protects the iron beneath it. It is the food-contact requirement specifically, not coating chemistry in general, that rules zinc out of a can.
Result — food cans are tin-plated rather than zinc-plated because zinc is more reactive than tin.