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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

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Deuterium: Methods of Preparation, properties and Uses

1H2 or 1D2. It occurs naturally in very small traces. The proportion present in naturally occurring hydrogen is in the approximate ratio: D: H~ 1:6000. It's nucleus consists of a proton and a neutron. However only a solitary electron is revolving around the nucleus. Its chemical properties are similar to those of protium but their reaction rates are different.

Methods of Preparation of deuterium

 

1. By Diffusion Process: It is possible to obtain deuterium directly from hydrogen gas by taking advantage of different rates of diffusion of the two isotopes. The lighter hydrogen diffuses more quickly than deuterium through a porous partition under reduced pressure. Lower the pressure, higher is the efficiency of the process.

 

The process of diffusion has been carried out in various diffusion chambers called Hertz diffusion units. Each diffusion units consists of a porous membrane.

 

When the mixture is led into the diffusion units under reduced pressure by the help of mercury diffusion pumps, the heavier deuterium diffuses less readily while lighter hydrogen diffuses at faster rates. This process is repeated several times till hydrogen gets collected on the left while deuterium on the right. The efficiency of this process could be increased by increasing the number of diffusion units.

 

 By fractional distillation of liquid hydrogen: By fractional distillation of liquid hydrogen, it is possible to result in enrichment of the last fraction in deuterium because deuterium boils at 23.5K while hydrogen boils at lower temperature of 20.2K.

 

 By electrolysis of heavy water: As water contains about one part of heavy water in 6000 parts, at first, the concentration of heavy water is increased by fractional electrolysis of water containing an alkali between nickel electrodes. For example 1 ml of heavy water is obtained from about 20 litres by this method.

 

From heavy water, it is possible to get deuterium by decomposing it with sodium, red hot iron or tungsten or by its electrolysis containing sodium carbonate.

2D2O ->Electrolysis 2 D2 + O2

Deuterium

D2O + 2Na ->  NaOD + D2

Sodium deuteroxide.

Deuterium obtained can be further obtained in purified state by the diffusion process.

Physical properties

 

Like hydrogen, deuterium is a colourless, odourless and tasteless gas which is insoluble in water and bad conductor of heat and electricity. The values of boiling point, melting point, vapour pressure, dissociation energy and latent heat of fusion are found to be lower for protium than deuterium.

Chemical properties

By virtue of its larger mass, deuterium reacts slower than hydrogen.

1. Burning in oxygen: Like hydrogen, it is combustible and burns in oxygen or air to give deuterium oxide which is also known as heavy water.

2 D2 + O2  -> 2D2O.

 

2. Reaction with halogens: Like hydrogen, it combines with halogens under suitable conditions to form their deuterides.

 

D2+ Cl2 --- (in light Deuterium chloride) ---- >  2 DCl

D2+ F2 ---- ( in dark Deuterium fluoride )---- > D2 F2

3. Reaction with nitrogen: Like hydrogen, it combines with nitrogen in the presence of a catalyst to form nitrogen deuteride which are also known as heavy ammonia or deutero ammonia.

3D2 + N2    - >  2ND3

 

4. Reaction with metals: Like hydrogen, it reacts with alkali metals at high temperatures (633K) to form deuterides

2 Na + D2    -- >    2 NaD

 

5. Addition reactions: Like hydrogen, it gives addition reactions with unsaturated compounds. For example, a mixture of deuterium and ethylene when passed over heated nickel, gives Ethylene deuteride which is saturated hydrocarbon like ethane.

C2H4 + D2  --- (Ni , 535K) CH2D -CH2D

Exchange reactions: Deuterium and hydrogen atoms undergo ready exchange with H2, NH3, H2O and CH4 deuterium slowly exchanges their hydrogens partially or completely at high temperatures.

H2 + D2  -><- 2 HD

2NH3 + 3D2 - 2ND3 + 3H2

H2O + D -   D2O + H2

CH4 + 2D2  -   CD4 + 2H2

C2H6 + 3D2  -  C2D6 + 3H2

Uses of deuterium

 

 It is used as tracers in the study of mechanism of chemical reactions.

 

 High speed deuterons are used in artificial radioactivity.

 

Its oxide known as heavy water (D2O) which is employed as moderator in nuclear reactor to
 
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