A student adds pieces of metals P, Q and R to solutions of salts of the same metals. A tick (✓) shows that a reaction happened. A cross (✗) shows that there was no reaction.
| P nitrate | Q nitrate | R nitrate | |
|---|---|---|---|
| P | – | ✗ | ✓ |
| Q | ✓ | – | ✓ |
| R | ✗ | ✗ | – |
(a) Place the metals in order of reactivity, most reactive first. [1]
(b) Iron rusts. State the two substances that must be present for rusting. [1]
(c) Explain how galvanising protects iron from rusting, even when the zinc coating is scratched. [2]
- (a) Q, P, R (all three in the correct order)(1)
- (b) water and oxygen (accept air for oxygen)(1)
- (c) zinc is more reactive than iron(1)
- (c) so zinc reacts / is oxidised / corrodes / loses electrons instead of iron (accept sacrificial protection; a barrier-only answer scores 0 for this mark)(1)
- Answer: (a) Q > P > R (b) water and oxygen (c) zinc more reactive, corrodes instead of iron
- Examiner tip: A barrier explanation alone does not score for galvanising when scratched — you must use the reactivity of zinc.