Viscosities and densities of concentrated aqueous NaOH/NaAl(OH)(4) mixtures at 25 degrees C

The dynamic viscosities (eta) and densities (rho) of aqueous NaOH/NaAl(OH)( 4) mixtures have been determined for solutions at constant ionic strength a nd total concentrations of [NaOH](T) less than or equal to 13.6 mol.kg-(1) and [Al (III)](T)/[Na+](T) less than or equal to 0.6 at 25 degreesC using a Ubbelohde viscometer and a vibrating tube densimeter, respectively. The vi scosities are precise to +/-0.1% and the densities to +/-5 x 10(-6) g.cm(-3 ). The densities of the mixtures at constant ionic strength vary linearly w ith substitution of OH- by Al(OH)(4)(-), consistent with Young's rule. This enables calculation of the density of the hypothetical aqueous solution of pure "NaAl(OH)(4)" at [Al(III)](T) less than or equal to 13 mol.kg(-1). Vi scosities of these mixtures, as with other electrolytes, are overestimated by Young's rule. Viscosities of the hypothetical pure "NaAl(OH)(4)" solutio ns (less than or equal to6 mol.kg(-1)) were accordingly determined by nonli near extrapolation, The eta values so obtained are unusually high but show a dependence on [NaAl(OH)(4)](T) similar to that of common electrolyte solu tions. An empirical correlation for the viscosities of NaOH/NaAl(OH)(4) mix tures is also given.