Question

A student needs to determine the diffusion coefficient of a gas in a liquid by measuring the rate of diffusion using a diffusion cell. If the student knows the initial concentration and final concentration of the gas in the cell, and the time it took for diffusion to occur, what is the diffusion coefficient of the gas in the liquid?

Answer 1

To determine the diffusion coefficient  D  of the gas in the liquid, the student can use Fick's second law of diffusion. Fick's second law states that the rate of change of concentration with respect to time is proportional to the second derivative of concentration with respect to position:C/t = D * C/xIn the case of the diffusion cell, we can simplify this equation by considering the one-dimensional case and assuming a constant diffusion area  A  and a constant diffusion path length  L . The equation becomes:C/t = -D * A *  Cf - Ci  /  L * V Where:C/t is the rate of change of concentration with respect to timeD is the diffusion coefficientA is the diffusion areaCi is the initial concentrationCf is the final concentrationL is the diffusion path lengthV is the volume of the liquidThe student can rearrange the equation to solve for the diffusion coefficient  D :D = -  C/t  * L * V /  A *  Cf - Ci  By plugging in the known values for the initial concentration  Ci , final concentration  Cf , time for diffusion  t , diffusion area  A , diffusion path length  L , and volume  V , the student can calculate the diffusion coefficient  D  of the gas in the liquid.