Deuterium oxide

October 15, 2018
I’m water’s big sibling.
What molecule am I?

Deuterium oxide (D2O), aka “heavy water”, is the form of water that contains two atoms of the 2H, or D, isotope. The term heavy water is also used for water in which 2H atoms replace only some of the 1H atoms. In this case, rapid exchange between the two isotopes forms twice as many “semiheavy” HDO molecules as D2O.

Harold Urey, the 1934 Nobel Prize laureate in chemistry, pioneered deuterium chemistry. In 1931, he and his colleagues at Columbia University (New York City) carefully distilled 5 L of liquid nitrogen to produce 1 mL of molecular deuterium. Shortly afterward, they produced D2O from ordinary water by using prolonged electrolysis.

For decades, D2O has been extremely useful in many chemical applications. The difference between a reaction rate in D2O solvent versus that in H2O often provides clues as to the reaction’s mechanism. This is especially important if water is one of the reactants.

In some nuclear reactors, D2O is used to slow down neutrons so that they react with fissionable 235U rather than nonfissioning 238U, thus eliminating the need for uranium enrichment. D2O is superior to H2O for this use because of its ≈6 times greater thermal neutron capture cross section.

Deuterium oxide fast facts

CAS Reg. No. 7789-20-0
Empirical formula D2O
Molar mass 20.03 g/mol
Appearance Colorless liquid
Melting point 3.8 ºC
Boiling point 101.4 ºC
Water solubility Miscible

Deuterium oxide hazard information

GHS classification*: not a hazardous substance or mixture

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

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