Write a note on heavy water.

Explanation

Heavy water is deuterium oxide. Its formula is `D_(2)O`. It contains heavier deuterium atoms in the place of normal hydrogen atoms of water molecule. It is prepared by the prolonged repeated electrolysis of `M/2 NaOH` solution. The electrolytic cell consists of a steel tank which acts as cathode. A perforated nickel sheet acts as anode and 0.5M NaOH solution acts as electrolyte. The electrolysis is carried in 7 stages. At the end of seventh stage 99% heavy water is obtained.
Properties:
(1) It reacts with `CaC_(2)` and liberated heavy acetylene.
`CaC_(2) + 2D_(2)O to C_(2) D_(2) + Ca(OD)_(2)`
(2) It reacts with `SO_(3)` and produced heavy sulphuric acid.
`SO_(3) + D_(2)O to D_(2) SO_(4)`
Hydrolysis reactions of salts with heavy water are called deuterolysis reactions.
Ex : `AlCl_(3) + 3D_(2)O to Al(OD)_(3) + 3DCl`
Uses : It is extensively used in nuclear reactiors as a moderator and in exchange reactions for the study of reaction mechanism.