Barium phosphite can have the molecular formula of
BaHPO3 or Ba(H2PO3)2 with molecular weights of
216.3021 and 296.2739 g/mol, respectively. It is the latter
that appears when a solution of phosphorous acid is
reacted with the carbonate:
BaCO3 +H3PO3 ? Ba(H2PO3)2 +H2O + CO2