A gas bubble of diameter \(3 \mathrm{~mm}\) is rising in a pool of a liquid. What is the mass transfer coefficient if the diffusion coefficient is \(2 \times 10^{-5} \mathrm{~cm}^{2} / \mathrm{s}\) ?

Note that the contact time is needed for finding the mass transfer coefficient. One way of approximating this is \[
\\text { Contact time }=\frac{\text { Bubble diameter }}{\text { Rise velocity }}\]
The rise velocity can be calculated using Stokes' law. Small bubbles are spherical and Stokes' law is a reasonable approximation here.