Handbook of Solvents - George Wypych - ChemTech - Ventech!

626 Victor Cherginets
Since even the pure salts containing mentioned hydroanions undergo the decomposition
at temperatures much lower then 350 o C with the formation of corresponding meta- or
pyro- salts, 68 equilibria [10.4.33] and [10.4.34] hardly take place in the absence of water vapor
in atmosphere over the melt.
The acidic properties of highest oxides of VI Group elements (Cr, Mo, W) were investigated.
23,48,49 Similarly to Group V oxides 43-48 CrO 3 and MoO 3 destructed the nitrate melt
with formation of Cr 2O 7 2- and Mo3O 10 2- , respectively. After the complete evolution of NO2,
e.m.f. values were close to 0.5 V, what was in a good agreement other studies. 43-48 The
potentiometric titration curves of the formed products contained only one drop of e.m.f. (or
pO). Chromate and molybdate ions were the final products of the neutralization reactions.
WO 3 was weaker acid and did not destruct the nitrate melt. Its titration was the one-stage
process resulting in the tungstate formation. The acidities of oxides increased in the order:
WO 3Sr>Ca>Pb of basicity decrease. The cation sequence was in a good correlation
with the electronegativity of metals. The proposed method of investigation had an essential
problem since the acids used for titration fixed oxide ions with the simultaneous
destruction of carbonate and formed insoluble chromates and phosphates with the majority
of cations studied. As it has been shown, 36,37 the addition of Ca 2+ into nitrate melts leads to
the shift of the interaction Cr 2O 7 2- -NO3 - to formation of nitronium cation and the melt decomposition
although the solution without Ca 2+ is stable. Such shift is explained by formation
of slightly insoluble CaCrO 4 in nitrate melt and has no relation to Ca 2+ acidity. It is
referred to the barium position in the sequence that gives evidence of the said complexes or
precipitates formation, since their acidic properties are substantially weaker than those of
Li + . The formation of the BaCrO 4 precipitate leads to approaching of Ba 2+ acidity to Li +
acidity. Probably, the same reason effected arrangement of others alkaline earth metals in
this sequence.
The relative strength of different Lux bases in nitrate melts was investigated. 54,55 The
bases studied were divided into two groups: the oxide ion group (OH - ,O 2- ,O 2 2- ) and the carbonate
ion group (CO 3 2- , HCO3 - , (COO)2 2- ,CH3COO - , HCOO - ). The bases belonging to the
first group have been assumed 54,55 to be completely transformed into O 2- .The members of
the first group of bases were weaker than the second group bases. From the thermal data it
may be seen that at experimental temperature (350 o C) all the second group bases are completely
broken down to carbonate. The differences between single bases may be attributed
to reduction properties - organic salts reduce nitrate ions to more basic nitrite ones and favor
the accumulation of oxide and carbonate ions in the melt over the stoichiometric ratio.