Rust is something new

The idea

Rusting of iron is a chemical change because it forms a new brown substance, rust, which is iron oxide.

The brown deposit

A new iron nail is shiny and grey. Left in the open for a few days, iron objects get a brown deposit.

Is the brown deposit still iron?

• Yes, it is iron with a little dirt on it
• No, it is a new substance
• It is only water

Iron or something new?

Slide to leave the nail in moist air. Then rub the brown deposit with a cloth, and compare it with iron.

Rusting is a chemical change

Rust does not look or feel like iron. It is a new substance, called iron oxide.

In the rusting of iron, a new brown-coloured substance called rust is formed. So rusting is a chemical change: it forms a new substance, iron oxide.

• Iron | Rust
• Colour | grey | brown
• Feel | hard, does not flake | flaky, rubs off

Notes

Rusting of iron is a chemical change. A new brown substance, rust, is formed. It is iron oxide.

Check yourself

An iron nail left in moist air gets a brown deposit. What kind of change is this?

What is the brown substance that forms on iron?

Which fact shows that rust is a new substance?

One shiny nail is bent. Another nail is left in moist air and turns brown. In which nail did a chemical change happen?

• Physical change, as only the colour changes. A new substance, rust, forms. More than the colour has changed.
• Chemical change, as a new substance forms — correct. Yes! Rust is a new substance.
• No change, as the nail is still there. The brown deposit is new, so a change has happened.
• Rust, which is iron oxide — correct. Yes! Rust is the new brown substance, iron oxide.
• Calcium carbonate, the white solid. That is the white solid in milky lime water.
• Carbon dioxide, a colourless gas. That is a gas. Rust is a brown solid.
• It sits on the surface of an iron nail. Sitting on the surface does not tell us. How it looks and feels does.
• It takes a few days to form. Slow or fast, that does not tell us if it is new.
• It looks and feels unlike iron — correct. Yes! Different properties show a new substance.
• The shiny nail that was bent. Bending only changes the shape. It is still iron.
• The nail that turned brown — correct. Yes! It formed a new substance, rust.
• Both of the nails. Only one of them formed a new substance.