Metals that change

The idea

Silver blackens by reacting with sulphur in air to form silver sulphide, copper gains a green coat of basic copper carbonate from moist carbon dioxide, and iron in moist air gets a brown flaky coating of rust.

Old things in air

A silver ornament, a copper vessel and an iron gate are left in the air for a long time.

What happens to them?

• Each changes in its own way
• Nothing happens to any
• They all turn black

Who gets what

Tap the metal each statement is about.

Three kinds of corrosion

Silver, copper and iron are all changed by the air. Silver blackens, copper becomes green and iron gets brown, flaky rust. Each coating is a new substance made by a chemical reaction of the metal.

Silver blackens by reacting with sulphur in air to form silver sulphide, copper gains a green coat of basic copper carbonate from moist carbon dioxide, and iron in moist air gets a brown flaky coating of rust.

Notes

Silver gets black silver sulphide, copper a green basic copper carbonate coat, iron brown flaky rust.

Check yourself

Silver articles become black because silver reacts with ... in the air.

The green coat on copper is ...

Copper gets its green coat by reacting with ...

The brown flaky coating on iron is called ...

• sulphur — correct. Yes!
• oxygen. The book says silver reacts with sulphur in the air to form silver sulphide.
• hydrogen. The book says silver reacts with sulphur in the air to form silver sulphide.
• silver sulphide. Silver sulphide is the black coating on silver.
• basic copper carbonate — correct. Yes!
• rust. Rust is the brown flaky coating on iron.
• sulphur in the air. Sulphur in the air is what blackens silver.
• dry nitrogen. The book says copper reacts with moist carbon dioxide in the air.
• moist carbon dioxide in the air — correct. Yes!
• rust — correct. Yes!
• silver sulphide. Silver sulphide is the black coating on silver.
• anode mud. Anode mud settles during electrolytic refining.