Chemical properties of heavy water

Hydrogen-deuterium exchange. When a compound containing hydrogen is treated with D₂O, its hydrogen atoms undergo an exchange with deuterium:

These exchange reactions have a genuinely useful analytical application: they let chemists determine how many "ionic" (exchangeable) hydrogen atoms a compound actually contains. For example, treating hypophosphorous acid with D₂O exchanges only one hydrogen atom:

Since only one of hypophosphorous acid's three hydrogens exchanges, this tells us that only one is ionisable -- i.e. that hypophosphorous acid is, despite its formula H₃PO₂, actually a monobasic acid (the other two hydrogens are bonded directly to phosphorus, not ionisable as protons).

Preparing other deuterium compounds. D₂O is also used as the deuterium source for preparing various deuterated compounds, by reacting it with the corresponding carbide, nitride or phosphide: …