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Grades 7–10 Intermediate About 20 min Version 1 Awaiting review Premium

What makes iron rust?

Rust is a flaky orange-brown substance that forms on iron. It is a new substance, iron oxide, made when iron reacts with oxygen from the air and water. Rusting is a slow chemical change called corrosion. In this experiment each test tube keeps one condition different, so you can find out exactly what iron needs in order to rust, and how it can be protected.

What you will learn

  • Show that iron needs both water and oxygen (air) to rust.
  • Describe how salt water affects the rate of rusting.
  • Explain how painting and galvanizing prevent rusting.

Before you start

  • Know the difference between physical and chemical changes.

Materials

  • Iron nails, a painted nail and a galvanized nail
  • Tap water (contains dissolved air)
  • Boiled water (air removed) with a layer of oil on top
  • Calcium chloride (a drying agent that removes water vapour)
  • Salt water

Equipment

  • 6 test tubes in a rack

Procedure

  1. Put an iron nail into Tubes A, B, C and D. Each tube has a different condition.
  2. Put a painted nail into Tube E and a galvanized (zinc-coated) nail into Tube F. Both have ordinary water and air.
  3. Use the timer to let the days pass, and check the nails every day.
  4. Record which nails rust, and how quickly.

How this simulation is simplified

  • Rusting times are typical values for a clean iron nail. Real rates depend on temperature, humidity and the nail.
  • The boiled water stays free of air because of the oil layer.