1. In studying the rate of leaching of a substance A from solid particles by a solvent B, we may postulate that the rate-controlling step is the diffusion of A from the particle surface through a liquid film thickness out into the main stream (see figure). The molar solubility of A in B is CA0, and the concentration in the main stream is CA. a) Obtain in a differential equation for CA as a function of z by making a mass balance on A over a thin slab of thickness z. Assume DAB is constant and that A is only slightly soluble in B. Neglect the curvature of the particle. b) Show that in the absence of chemical reaction in the liquid phase the concentration profile is linear. c) Show that the rate of leaching is then given by NAAz=DAB(CA0CA)/