Study of obstruction effect and activation energy for tracer diffusion of chromium ions in agar gel containing transition metal sulphates

The effect of concentration of ions on obstruction effect and activation energy for the tracer diffusion of chromium ions in agar gel medium containing NiSO4, CuSO4 and ZnSO4 is studied using zone diffusion technique. The obstruction effect is studied by measuring diffusion coefficient at varying gel percentage ranging from 2.5-4.0% at 25 °C. The activation energy in same supporting electrolytes is investigated using 2.5% agar gel over the temperature range of 25 to 45 °C. The activation energies were obtained by the least square fitting data of the diffusion coefficients in the Arrhenius plot. It is observed that both parameters, extent of obstruction (α) and activation energy (E) decreases with an increase in charge density of the cation of the supporting electrolyte. These observations are explained on the basis of competitive hydration between ions and agar molecules and the distortion in the water structure caused by ions and agar molecules, respectively.