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Heavy water (D2O) is the oxide of heavy hydrogen. One part of heavy water is present in 5000 parts of ordinary water. It is mainly obtained as the product of electrolysis of water, as D2O does not undergo electrolysis as easily as H2O.
D2O is a colorless, odorless and tasteless liquid. However, there is a marked difference between physical properties of water and heavy water as shown in Table 4.2.
The cleaning capacity of soap is reduced when used in hard water. Soaps are sodium or potassium salts of long chain fatty acids (e.g., coconut oil). When soap is added to hard water, the divalent magnesium and calcium ions present in hard water react with soap. The sodium salts present in soaps are converted to their corresponding magnesium and calcium salts which are precipitated as scum/precipitate.
When compounds containing hydrogen are treated with D2O, hydrogen undergoes an exchange for deuterium
2NaOH + D2O → 2NaOD + HOD
HCl + D2O → DCl + HOD
NH4Cl + 4D2O → ND4Cl + 4HOD
These exchange reactions are useful in determining the number of ionic hydrogens present in a given compound.
For example, when D2O is treated with of hypo-phosphorus acid only one hydrogen atom is exchanged with deuterium. It indicates that, it is a monobasic acid.
H3PO2 + D2O → H2DPO2 + HDO
It is also used to prepare some deuterium compounds:
Al4C3 + 12D2O → 4Al(OD)3 + 3CD4
CaC2 + 2 D2O → Ca(OD)2 + C2D2
Mg3N2 + 6D2O → 3Mg(OD)2 + 2 ND3
Ca3P2 + 6D2O → 3Ca(OD)2 + 2PD3
1. Heavy water is widely used as moderator in nuclear reactors as it can lower the energies of fast neutrons
2. It is commonly used as a tracer to study organic reaction mechanisms and mechanism of metabolic reactions
3. It is also used as a coolant in nuclear reactors as it absorbs the heat generated.
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