The rate at which a solid dissolves varies directly as the amount of undissolved solid present in the solvent and as the difference between the saturation concentration and the instantaneous concentration of the substance.
a saturated solution of salt in H2O will hold approximately 3 lb salt/gal. A block of salt weighing 60 lb is placed into a vessel containing 100 gal of H20. In 5 mins., 20 lb of salt were dissolved. (a) How much salt will be dissolved in one hour? (b) When will 45 lb of salt be dissolved?