An environmental monitoring station uses steel housings beside a salt marsh. Salt spray reaches the housings, and their surfaces may be scratched during maintenance.
A technician places identical steel samples in different conditions for 28 days.
Any rust is removed before the final mass is measured.
| Sample | Conditions | Decrease in mass after 28 days (g) |
|---|---|---|
| 1 | dry air | 0.00 |
| 2 | boiled water covered with a layer of oil | 0.00 |
| 3 | tap water open to the air | 0.18 |
| 4 | salt water open to the air | 0.46 |
Explain the results.
The technician tests three treatments on identical steel panels at the monitoring station. The paint and zinc coatings each have a scratch of the same size.
The zinc coating remains on the panel throughout the test.
| Treatment | Mass of steel lost after one year (g) |
|---|---|
| no coating | 2.6 |
| paint coating | 0.7 |
| zinc coating | 0.0 |
Explain which treatment should be used for the steel housings. Use data from the table and your knowledge of corrosion.
136 exam-style questions on OCR GCSE Chemistry 6.1 Improving processes and products, covering 6.1.1 Extracting metals industrially and by electrolysis, 6.1.2 Life cycle assessment and recycling, 6.1.3 Biological methods of metal extraction, 6.1.4 The Haber process and the production of fertilisers, 6.1.5 Alloys and their uses, 6.1.6 Corrosion and its prevention, 6.1.7 Comparing and selecting materials, and 6.1.8 Industrial conditions, rate and position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.