Ionic dissociation of aqueous hydrobromic acid. Part 2.—Estimate from proton magnetic resonance data at 6–60° C

Abstract

Proton nuclear magnetic resonance measurements have been made on aqueous hydrobromic acid solutions at 6–60°C and over a concentration range ≈ 1–20 mol kg^–1. The data have been interpreted according to the Gutowsky and Saika method, considering several options for the limiting slopes at low and high concentrations. The chemical shift of hydronium ions relative to water, S_H3O⁺, can be obtained from extrapolation of data to zero concentration [option (a)], or from a correlation of data on other acids with the anion volume [option (b)]. The chemical shift of the undissociated acid, s_HBr, can be equated with that of liquid hydrogen bromide [option (c)], or can be obtained from the data at the highest aqueous acid concentrations [option (d)]. The combination of options (a) and (d) is preferable to the other combinations of options. The data yield a mean degree of association over the temperature range studied of 2% at 4 mol kg^–1, of 6% at 8 mol kg^–1, of 11% at 12 mol kg^–1, of 20% at 16 mol kg^–1 and of 34% at 20 mol kg^–1(with a relative uncertainty of ±25%).