Barium Nitrite, Ba(NO₂)₂

Barium Nitrite, Ba(NO₂)₂, is best obtained by the decomposition of silver nitrite by barium chloride. It is also formed in other ways, for example by the action of nitrous acid vapours on barium hydroxide solution or barium carbonate, by careful calcination of the nitrate and removal of barium oxide and nitrate, or by a combination of these two methods; by reduction in the dry state by copper, cuprous oxide, oxalates, or other reducing agents; by the action of sodium nitrite on barium chloride in a limited amount of water; and by the electrolytic reduction of barium nitrate solution.

The properties of barium nitrite have been carefully examined by Oswald, and also by Ray. The anhydrous salt has a density of 3.52 at 0° C., melts at 217° C., and decomposes at 235° C. From solution it crystallises as the monohydrate in glistening, faintly yellow needles, isomorphous with the strontium salt and of density 3.109. This hydrate is stable in air, melts at 184° C. with partial hydrolysis, and may be dehydrated in vacuo over phosphorus pentoxide. It is difficult to remove all the water of crystallisation. The powdered salt dried in the steam-oven has a composition of approximately Ba(NO₂)₂.½H₂O. Fock obtained the anhydrous salt in hexagonal crystals by slow evaporation.

The following values have been obtained for the solubility of the monohydrate at different temperatures: -

Temperature, °C	0	10	20	30	40	50	60	70	80	90	100	110
Grams Ba(NO2)2.H2O in 100 grams water.	63.5	69.5	79.5	93	113	136	170	202	254	461	461	765

The cryohydric temperature is -6.5° C., and the cryohydrate contains 34.5 per cent, of the nitrite.

The solubility of barium nitrite is diminished by alcohol, and in 90 per cent, alcohol the salt is practically insoluble. The aqueous solution has an alkaline reaction. It is stable unless acidified, when it is readily oxidised. Concentrated aqueous solutions undergo hydrolysis at 100° C.

Several double salts are known: Ba(NO₂)₂.2AgNO₂.H₂O, 2Ba(NO₂)₂.3Hg(NO₂)₂.5H₂O, containing the complex bivalent anion Hg(NO₂)₄^2-, Ba(NO₂)₂.2KNO₂, Ba(NO₂)₂.2KNO₂.H₂O, 2Ba(NO₂)₂.CsNO₂, Ba(NO₂)₂.2CsNO₂.H₂O, Ba(NO₂)₂.AgNO₂.3CsNO₂.2H₂O, and Ba[Cu(NO₂)₂OH]₂.