Absorption of Sound in Manganous Sulfate Solutions

Abstract

The absorption of sound in MnSO4 solutions was studied over the frequency range 1 to 55 Mc as a function of concentration, temperature, dielectric constant, and with D2O as solvent. The absorption maximum in the range 1 to 10 Mc was verified, and also a secondary relaxation peak, not previously reported, was observed near 30 Mc. The primary relaxation frequency was decreased when the dielectric constant was lowered, while the secondary relaxation frequency was increased. The absorption cross section was increased when the dielectric constant was decreased. The primary relaxation frequency increased with increasing temperature following Arrhenius' equation. The activation energy was determined for both isodielectric and isocomposition solutions. Substitution of D2O as a solvent had no effect on the primary relaxation frequency but increased the absorption cross section. The secondary relaxation was not observed in D2O solutions. These results indicate that the hydrogen ion is not involved in the rate-determining reaction causing the observed relaxation effects. Furthermore, the results seem to rule out the reaction between two ions of unlike sign as the rate determining step in the primary relaxation process and to make the reaction between ions of like sign improbable. All observed data can be explained on the assumption that the reaction is between two dipole molecules.