A detailed study of highly concentrated aqueous alkaline aluminate sol
utions has been made by hydrogen electrode potentiometry in cells with
liquid junction at 25 degrees C in 8 M Na(ClO4) media. Measurements w
ere performed over the total concentration ranges 0.1 M < [NaOH](T) <
4.0 M and 0.02 M < [Al-III](T) < 3.2 M, and at total concentration rat
ios of 6.92 greater than or equal to [OH-](T)/[AL(III)](T) greater tha
n or equal to 4.3. Nernstian electrode behaviour was observed at [NaOH
](T) less than or equal to c. 2 M in pure NaOH/NaClO4 mixtures. At low
[Al-III](T) the data were consistent with the formation of only the w
ell known Al(OH)(4)(-) (aq) species but there is clear evidence of a s
ystematic release of hydroxide as [Al-III](T) and [NaOH](T) increase.
The data are consistent with the formation of polymeric aluminate comp
lexes having a stoichiometry of Al-q(OH)(3q-r)(r+) (q = 4-7, q+r = 1 o
r 2). However, unequivocal identification of these species is difficul
t on account of strong correlations in the data and the possible effec
ts of ion-pairing.