Viscosities and Densities of Highly Concentrated Aqueous MOH Solutions (M⁺ = Na⁺, K⁺, Li⁺, Cs⁺, (CH₃)₄N⁺) at 25.0 °C

Abstract

The absolute (dynamic) viscosities (η) and densities (ρ) of carbonate-free aqueous tetramethylammonium and alkali metal hydroxides have been determined up to saturation concentrations ([NaOH] ≤ 19.l M, [KOH] ≤ 14.1 M, [LiOH] ≤ 4.8 M, [CsOH] ≤ 14.8 M, and [(CH 3 ) 4 NOH] ≤ 4.2 M) at 25.00 °C using a Ubbelohde viscometer and a vibrating tube densitometer, respectively. The viscosities are believed to be precise to within 0.1% and the densities to within 5 × 10 - 6 g cm - 3 . Densities of isoplethic MOH solutions increase in the order of (CH 3 ) 4 N + < Li + < Na + < K + ≪ Cs + . Viscosities for [MOH] < 4 M solutions increase in the reverse order, but the viscosities of CsOH solutions become extremely large at very high concentrations. The shape of the density vs concentration function of (CH 3 ) 4 NOH solutions is also quite different when compared with the alkali metal hydroxide solutions. Density data were fitted up to the highest concentrations using the Masson equation. Viscosity vs concentration functions are represented in the form of a fifth-order (empirical) polynomial.