Viscosities and Densities of Concentrated Aqueous NaOH/NaAl(OH)4 Mixtures at 25 °C

Abstract

The dynamic viscosities (η) and densities (ρ) of aqueous NaOH/NaAl(OH)4 mixtures have been determined for solutions at constant ionic strength and total concentrations of [NaOH]T ≤ 13.6 mol·kg-1 and [Al(III)]T/[Na+]T ≤ 0.6 at 25 °C using a Ubbelohde viscometer and a vibrating tube densimeter, respectively. The viscosities are precise to ±0.1% and the densities to ±5 × 10-6 g·cm-3. The densities of the mixtures at constant ionic strength vary linearly with 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 ≤ 13 mol·kg-1. Viscosities of these mixtures, as with other electrolytes, are overestimated by Young's rule. Viscosities of the hypothetical pure “NaAl(OH)4” solutions (≤6 mol·kg-1) were accordingly determined by nonlinear extrapolation. The η values so obtained are unusually high but show a dependence on [NaAl(OH)4]T similar to that of common electrolyte solutions. An empirical correlation for the viscosities of NaOH/NaAl(OH)4 mixtures is also given.