Question

How is heavy water prepared? Compare its physical properties with those of ordinary water.

Answer 1

Preparation of heavy water:

Heavy water can be prepared by exhaustive electrolysis of water. Exhaustive electrolysis means electrolyzing water for longer duration in a cell.

This method is based upon the principle that when ordinary water is electrolysed, protium is liberated much more readily than deuterium As the electrolysis continues the concentration of heavy water in ordinary water increases and pure $D_{2}O$ is eventually obtained.

Comparison of physical properties of heavy water and ordinary water:

	Physical property	$H_{2}O$	$D_{2}O$
(i)	Molar mass ($g/mol$)	18.0151	20.0276
(ii)	Melting point ( K )	273.0	276.8
(iii)	Boiling point ( K )	373	374.4
(iv)	Density in $g.c{m}^{-3}$ (at 298 K)	1.0000	1.1059
(v)	Enthalpy of vapourisation $(kJ.mo{l}^{-1}$)	40.66	41.61
(vi)	Dielectric constant $(C^2.N{m}^2$)	78.39	78.06

• Heavy water is heavier than ordinary water, it can be verfied from their density values, i.e, Density in $g.c{m}^{-3}$(at 298 K)
• For ordinary water =1.0000
• For heavy water =1.1059
• Dielectric constant of heavy water is lower than that of oridinary water, so, ionic compounds will be more soluble in ordinary water than heavy water.
• High melting and boiling point of heavy water indicates it have stronger intermolecular forces of attraction than ordinary water.