The instability of magnesium nitrite, even when dissolved
in water, has not engendered any usage in industry.
Magnesium nitrite has the formula of Mg(NO2)2 and
the molecular weight of 116.3164 g/mol. It can be made
by the usual double decomposition reaction of sodium
nitrite and CaCl2:
2NaNO2 (aq) ＋ MgCl2?Mg(NO2)2 (aq) ＋ 4NaCl (aq)
It forms a trihydrate having a molecular weight of
170.3626 g/mol. Magnesium nitrite is soluble in water
and the solution must be evaporated at very low temperatures
to obtain crystals. The solution is stable and is
slightly hydrolyzed in the cold but at 60° and above it
evolves oxides of nitrogen. Its CAS number is 15070-34-5 and it occurs as white, hydroscopic crystals that
must be protected from moisture to prevent decomposition.
The trihydrate, when heated, forms the monohydrate
at 100 °C and then decomposes to NO ＋ NO2
and MgO at >130 °C. It is soluble in alcohol.
