Sound absorption reduction in 0.02 M MgSO4 solutions with the addition of NaCl has been measured at 25°C and 1 atm, using a 100‐liter titanium spherical resonator. Using the equation Kurtze and Tamm [Acustica 3, 33 (1953)] developed, a/a0 = [MgSO4]/(MgSO4] + F[NaCl]), our measured results for concentration ratios of [NaCl]/[MgSO4] = 0, 1, 2, 4, and 6 yields F = 0.146 ± 0.033, contrary to Kurtze and Tamm's value, 0.21. Our value of F agrees well with the 0.134 value from theoretical calculations including effects of ionic strength and ion‐pairing of MgSO4, NaSO4, and MgCl+, using dissociation constants of 0.0062, 0.1, and 0.178, respectively, for these salts. Theory also shows that F is not a constant, but a variable depending on [MgSO4] and [NaCl]/[MgSO4]. If the dissociation constants of the unsymmetrical salts are doubled, F = 0.093. F is 0.052 if only ionic strength effects are included, i.e., no unsymmetrical ion‐pairing. This technique therefore can be used to quantitatively study ion‐pairing of unsymmetrical salts. [Work supported by ONR and NSF.]

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