Abstract:

Ice was grown from aqueous solutions of NH4F, NH4F+HF and NH4F+NH3. The d.c. conductivity of the samples was measured in a field of 10-20 V/cm and the concentration of F and NH3 was determined in the melted ice, since the latter gives information on the segregation law for the two electrolytes in mixed solutions. At a given temperature (-17°C) the conductivity of ice is a function of the ratio [F]/[NH3] over a wide range of concentrations, where [F] and [NH 3] are the total concentration of acid and base in the samples, as expected for a system of a solution of a weak acid and a weak base. From the slope of the conductivity against [F]/[NH3] plot, approximate values of KF/√K0 and KF/KNH3 are derived (K0 = [H3 +][OH-], K F = [F-][H3O+]/[HF], K NH3, = [NH+ 4][OH-][NH4OH] in ice). The results do not agree with previous estimations. The discrepancy for K F/√K0 is reduced if we suppose that the conductivity of pure ice is two or three times lower than that previously assumed. The mobility of the proton is then 22 or 32 times lower than the estimate of Eigen and De Maeyer and consequently the value of K F/√K0 obtained previously would be 23 or 33 times higher. Our value for KF/KNH3 suggests a lower value of the ratio of mobilities for H3O+ and OH-than that proposed by Eigen and De Maeyer.