Describe an activity to show that air and water are both needed for iron to rust. Give two ways to prevent rusting.

1. 1 · Open in one line. Rusting is the corrosion of iron to reddish-brown hydrated iron oxide; it needs air and water.
2. 2 · Set up three tubes.
   • Tube 1: nails in tap water, open to the air.
   • Tube 2: nails in boiled distilled water with a layer of oil, corked.
   • Tube 3: nails with anhydrous calcium chloride, corked.
3. 3 · Draw the three tubes. Draw three test tubes side by side with nails inside. Label: air, water, boiled distilled water, layer of oil, cork, anhydrous calcium chloride, rusted nail.
4. 4 · Give the result. Only the nails in tube 1 rust. Tube 2 has no air, and tube 3 has no moisture. So both air and water are needed.
5. 5 · Prevention.
   • Painting, oiling or greasing to keep air and water away.
   • Galvanising with zinc, or making an alloy such as stainless steel.
6. 6 · Link to real life. Iron window grills are painted before the monsoon, and stainless steel vessels never rust.
7. 7 · Close in one line. So keeping either air or water away stops rusting.

Scoring tip: Say why each of the other two tubes shows no rust (no air, no moisture). That reasoning carries the marks.