Sodium hypophosphite, NaH₂PO₂

The Sodium hypophosphite is formed by the interaction of sodium hydroxide and phosphorus:

P₄+3NaOH+3H₂O =3NaH₂PO₂+PH₃.

It can also be obtained by decomposing the calcium or barium salt by the action of sodium carbonate in alcoholic solution.

Sodium hypophosphite is a powerful reducer. On heating it evolves phosphine, the reaction being often so violent as to cause explosion:

5NaH₂PO₂ =Na₄P₂O₇+NaPO₃+2PH₃+2H₂.

At 21.5° C. the heat of formation from sodium hydroxide and the acid is 15.16 Cal., and that from the elements in solution is 198.4 Cal. The electric conductivity has been studied by Arrhenius.