A large amount of salt is added to the bottom of a beaker containing freshwater. The salt covers the bottom of the beaker uniformly and the depth of water above the salt is 10 cm. If the solubility limit of salt in water is 0.357 g/cm 3 and the diffusion coefficient is 10-9 m2 /s: a) Estimate how long it is before the presence of the free surface is 'felt' by the diffusing salt. b) For times much shorter than calculated in (a), derive an expression for the salt mass flux at the salt/water interface as a function of time. What is the flux after 1 hour? c) What is the salt concentration at the water surface 2 weeks after the experiment began? d) Estimate the time required for 'full' mixing of the salt in the beaker, assuming this occurs when the surface salt concentration is 95% of the solubility limit.

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Salt Diffusion in a Beaker a Time to Feel the Free Surface This problem involves diffusion across a ... View the full answer