Ultrasonic Absorption in Sodium Metaborate Solution

Abstract

The kinetics of reaction in the dilute aqueous solution of sodium metaborate have been studied by ultrasonic absorption measurements over the frequency range from 50 kc/sec to 75 Mc/sec. Single relaxation frequencies have been observed in 0.05, 0.1, and 0.2M at 25°C and in 0.1M at 35°C, and the absorption mechanism has been assigned to be due to the hydrolysis of metaborate ion. The corresponding forward and backward rate constants calculated for the reaction BO2−+H2O⇌HBO2+OH− are 4.11×103 sec−1 and 2.36×108M−1 sec−1 at 25°C for 0.05M solution, respectively. From the magnitude of the relaxational acoustic absorption per wavelength, the partial molal volume change ΔV° for the process is calculated to be 6.83 cm3/mole at 25°C for the 0.05M solution. The temperature dependence of the relaxation frequency indicates that the energies of activation for the reaction are 12.6 and 1.31 kcal/mole for the forward and backward reactions, respectively.