Describe Properties of Chromium

Properties of Chromium (Cr):

Physical Properties:

1. The metal is silvery white and crystalline.
2. It is very hard and brittle
3. It melts at 2113K.

Chemical Properties:

Action of air: It is unaffected by air at ordinary temperatures.

When heated to very high temperature at about 2000°C it is oxidized to chromic oxide.

• 4Cr + 3O₂ → 2Cr₂O₃

Action of Water: There is no action at ordinary temperatures. However it decomposes steam at red heat to give chromic oxide and hydrogen.

• 2Cr + 3H₂O → Cr₂O₃ + 3H₂

Action of Acids: It dissolves in dilute hydrochloric acid and sulphuric acid to liberate hydrogen and forms chromous salts.

• Cr + 2HCl → CrCl₂ + H₂↑
• Cr + H₂SO₄ → CrSO₄ + H₂↑

With hot concentrated sulphuric acid it gives chromic sulphate and liberates sulphur dioxide.

• 2Cr + 6H₂SO₄ → Cr₂(SO₄)₃ + 3SO₂ + 6H₂O

Dilute nitric acid does not attack the pure metal while concentrated acid renders it inactive or passive i.e., it does not show its usual reactions.

Action with Halogens: Chromium combines directly with fluorine and dry chlorine to give chromium (III) halides.

• 2Cr + 3F₂ → 2CrF₃
• 2Cr + 3Cl₂→ 2CrCl₃