Ultrasonic Investigation on Kinetics of Ionic Reaction in Sodium Phosphate Solution

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Abstract
The velocity of sound in sodium phosphate solutions has been studied in the frequency range 2.5–6.5 Mc/sec at concentrations varying from 0.01 to 0.25M. The normal dispersion below 0.1M and the abnormal dispersion above 0.11M have been observed. In the former concentration region the dependence of concentration on the relaxation frequency gave the equilibrium constant which was in excellent agreement with that of the hydrolysis of PO43− and made clear the mechanism responsible for dispersion. The corresponding forward and reverse rate constants were calculated using the relaxation time in solution and the dissociation constants of the acid and water at 25°—35°C. The activation energy was also calculated from the temperature dependence of rate constants. The discussion was extended to the effect of dielectric constant and hydrogen‐ion concentration on the dispersion.