Preventing rusting by galvanising
4 marks · NormalThe table shows observations of iron nails kept under different conditions for two weeks.
| Test tube | Condition | Rust observed after 2 weeks? |
|---|---|---|
| A | Nail in dry air (no water) | No |
| B | Nail in boiled water, oil layer on top (no air) | No |
| C | Nail in ordinary water, exposed to air | Yes |
Use the data to state the two conditions needed for rusting.
Suggest why no rust formed in test tube B.
Explain why rusting happened in test tube C.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Both water and air (oxygen) are needed.
(b) There was no air (oxygen) present in test tube B.
(c) Rusting happened in C because both air (oxygen) and water were present.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies water is needed for rusting.
B2 (a) · 1 mark · Identifies air/oxygen is needed.
B3 (b) · 1 mark · Correctly states there was no air/oxygen in tube B.
B4 (c) · 1 mark · Correctly explains both water and air were present in C.
Worked solution
a) The data shows that rust only formed when both ordinary water and air (oxygen) were present (test tube C). So, the two conditions needed are water and air (oxygen).
b) No rust formed in B because there was no oxygen: the boiled water removed dissolved air, and the oil layer kept air out.
c) Rusting happened in C because the nail was exposed to both air and water.