Corrosion

Question 1 Define the term corrosion?

Question 2 What is meant by rusting of iron?

Question 3 State the conditions necessary for rusting of iron?

Question 4 State the ways to prevent the rusting of iron?

Question 5 Name the metal used for galvanising iron?

Question 6 Why copper objects lose their shine after sometime?

Question 7 Why silver articles became black when exposed to air?

Question 8 Why gold ornaments look new even after several years of use?

Corrosion

The eating up of metals by the action of air, moisture or a chemical on their surface is called corrosion.

The copper objects lose their shine after sometime due to the formation of copper oxide on them. When a copper object reacts with moist carbon dioxide, it loses its shiny brown surface and gains a green coat(basic copper oxide which is a mixture of copper carbonate and copper hydroxide)

Silver articles became black after sometime when exposed to air because it react with sulphur in air to form a coating of silver sulphide.

The corrosion of iron is called rusting. When an iron object is left in damp air for a considerable time, it gets covered with a red brown flaky substance called rust.

Rust is hydrated iron(III) oxide. The formula of rust is Fe₂O₃.nH₂O

The two conditions necessary for rusting of iron is presence of air and water.

Prevention of Rusting

1) By painting

2) By applying grease or oil.

3) By galvanisation : The process of depositing a thin layer of zinc metal on iron.

4) By tin plating and chromium plating.

5) By alloying it