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