Steel guide rails for outdoor sliding doors may be scratched during use.
A company tested two coatings, P and Q. One coating was paint and the other was zinc. The labels identifying the coatings were lost.
Coated steel samples were exposed to air and rain for six months.
| Coating | Condition before exposure | Observations after six months |
|---|---|---|
| P | Intact | No rust formed on the steel. |
| P | Scratched to expose the steel | Rust formed at the scratch. |
| Q | Intact | No rust formed on the steel. |
| Q | Scratched to expose the steel | No rust formed on the steel. Coating Q corroded next to the scratch. |
Explain the results in the table and state which coating is zinc. Use results from the table to support your answer.
After several years, all of coating Q has corroded away from a scratched guide rail.
Suggest what will happen to the steel if the guide rail remains exposed to air and rain. Explain your answer.
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.