A manufacturer tests two coatings, P and Q, on identical steel brackets used outdoors. One coating is paint and the other is zinc.
The brackets are exposed to air and sprayed with water each day. Before the test, one bracket with each coating is scratched through to the steel.
| Coating | Coating scratched | Area of rust at the end of the test in cm² |
|---|---|---|
| P | No | 0.0 |
| P | Yes | 2.6 |
| Q | No | 0.0 |
| Q | Yes | 0.0 |
Explain how the results show which coating is paint and which coating is zinc.
The mass of coating Q on another bracket was 18.6 g before the test and 17.9 g after the test.
Explain, using the data, why coating Q must be renewed after several years.
118 exam-style questions on AQA GCSE Chemistry 10.3 Using materials, covering 10.3.1 Corrosion and its prevention, 10.3.2 Alloys as useful materials, and 10.3.3 Ceramics, polymers and composites. Each one has a worked solution and a mark scheme showing where the marks go.