Dielectric Relaxation of Dilute Aqueous NaOH, NaAl(OH)4, and NaB(OH)4

Abstract

The complex dielec. permittivity of aq. NaOH (c ≤ 2M) and of dil. (≤0.6M) NaAl(OH)4 and NaB(OH)4 solns. in NaOH ([Na] = 1M) at 25° has been detd. in the frequency range 0.2 ≤ ν/GHz ≤ 20. All spectra could be represented by a single Cole-Cole relaxation time distribution attributed to the cooperative relaxation of the solvent. The concn. dependence of the effective hydration no. of OH- has been detd. For aluminate and borate solns., the deduced parameters, viz. effective cond. κe, static permittivity ε, relaxation time τ, and distribution parameter α, suggest a 1:1 replacement of hydroxide by aluminate and borate accompanied by a release of bound water. The lack of an ion-pair relaxation process despite notable ion assocn. suggests that rapid proton exchange is important not only for the dynamics of OH- but also for Al(OH)4- and B(OH)4-.