BARIUM HYPOPHOSPHITE. 135
and wash it with a little cold water. Dry the product in a por-
celain dish and then heat it with a free flame until carbon
dioxide ceases to escape. Recrystallize the crude sodium carbonate
thus obtained from five times its weight of water, and wash the
crystals with a little water. Concentrate the mother-liquor to
obtain another crop of crystals. Recrystallize. Yield, about 40 g.
A solution of the sodium carbonate, after being acidified with
nitric acid, ought not to show more than a slight cloudiness with
silver nitrate.
(g) Phosphoric Acids.^1
Structural formulas can be written as below for orthophosphoric acid,
H3PO4, phosphorous add, H3PO3, and hypophosphorous add, H3PO2, if it is
taken into consideration that the first acid is tribasic, the second dibasic, and
the third monobasic, and if it is assumed, although this is by no means proved,
that all the hydroxyl hydrogens, and only these, can be replaced by metals
in the formation of salts.O=P-OH
XOH
Orthophosphoric acid.O=P-OH
XOH
Phosphorous acid.O = P-H
XOH
Hypophosphorous acid.
The reducing action of the last two acids would accordingly consist in
taking up oxygen which would enter between the phosphorus atom and the
hydrogen atoms.
If it is not assumed that all the hydroxyl hydrogens are replaceable, then
the formulas P(OH) 3 and HP(0H)2 become possible, according to which phos-
phorous and hypophosphorous acids are derived from tervalent phosphorus.
It may be, as in the case of sulphurous acid, that both formulas have a cer-
tain justification (compare p. 126 and Nos. 155 and 156).
By the loss of water from one and from two molecules of orthophosphoric
acid, meta-phosphoric and pyro-phosphoric acids respectively are obtained:O=P-OH HO-P-0-P-OH
HO/ XOH
Metaphosphoric acid. Pyrophosphoric acid.
HYPOPHOSPHOHIC ACID, H 2 PO 3 , which was formerly written H 4 P 2 O 6 , has
recently been found to have a molecular weight corresponding to the smaller
molecule, and is presumably derived from quadrivalent phosphorus.
- Barium Hypophosphite, Ba(H 2 PO 2 ) 2 • H 2 O.
Salts of hypophosphorous acid are formed by the action of phosphorus
on warm, aqueous solutions of strong bases:
4 P + 3 KOH + 3 H 2 0 = 3 KH 2 PO 2 + PH 3.(^1) Cf. Note 2, p. 126.