Corrosion of Metals Quiz

1. Which two conditions are both essential for the rusting of iron to occur?

• A. Oxygen and water
• B. Oxygen and carbon dioxide
• C. Water and salt only
• D. Heat and moisture

2. How does painting a steel object prevent rusting?

• A. It reacts chemically with the iron surface
• B. It acts as a barrier method by excluding oxygen and water
• C. It converts iron(II) oxide to iron(III) oxide
• D. It reduces the reactivity of the steel

3. In galvanising, zinc protects iron from rusting through two mechanisms. What is the primary reason zinc can offer sacrificial protection?

• A. Zinc is less reactive than iron and forms a stronger oxide layer
• B. Zinc is more reactive than iron, so it loses electrons preferentially and corrodes instead
• C. Zinc forms an impermeable barrier coating on the iron surface
• D. Zinc reacts with oxygen to form a catalyst that prevents rusting

4. Which statement correctly describes the difference between barrier methods and sacrificial protection?

• A. Barrier methods work by excluding oxygen and water, whilst sacrificial protection relies on a more reactive metal being oxidised instead
• B. Barrier methods use zinc, whilst sacrificial protection uses paint or grease
• C. Barrier methods are temporary, whilst sacrificial protection is permanent
• D. Barrier methods prevent water absorption, whilst sacrificial protection prevents oxygen absorption

5. A piece of iron is coated with zinc. After scratching through the zinc coating, the exposed iron does not rust. Explain why, using the reactivity series.

• A. Iron becomes more reactive than zinc due to the scratch, so zinc corrodes instead
• B. The zinc coating still prevents water from reaching the exposed iron
• C. Zinc is more reactive than iron, so it preferentially loses electrons and corrodes whilst protecting the iron
• D. The scratch allows air to circulate, drying the surface and preventing rust formation