MEASUREMENTS OF SELF-DIFFUSION IN AQUEOUS SOLUTIONS OF SODIUM DIHYDROGEN PHOSPHATE

Abstract

Measurements of self-diffusion in aqueous solutions of sodium dihydrogen phosphate have been made using P32 as tracer. The method involves the preparation of two similar solutions differing only in the fact that one is "labelled" by means of the P32 isotope. A capillary cell is filled with the radioactive solution and immersed in a relatively large volume of inactive solution, maintained at a constant temperature. After diffusion has proceeded for a measured length of time, the cell is removed and the radioactivity of the liquid remaining in it measured by counting. The self-diffusion coefficient may be calculated from the length of the capillary cell, the period of diffusion, and the ratio of the final activity to the original activity. The method was checked by repeating some work on the self-diffusion of Na+ in sodium iodide solution. Self-diffusion measurements were made with sodium dihydrogen phosphate solutions of several concentrations between 1.0 and 10−4 molar.