VOL. 5, NO. 3
EMEKSON AND CABMISTRY.PA= I
279
A SIMPLE ILLUSTRATION OF THE LAW OF MASS ACTION A simple and convenient lecture method for illustrating the application of the law of mass action in suppressing the ionization of a weak acid by its sodium salt is obtained by using acetic acid and sodium acetate with methyl red as an indicator. Dilute 0.5 cc. of 30% U. S. P. acetic acid with 100 cc. of water. To a few cc. of this solution add a few drops of the methyl red indicator. A characteristic violet-red color due to the hydrogen ion will develop. I am using the LaMotte methyl red, pH 4.4-0. For convenience I dissolved 0.02 g. of the indicator in 100 cc. ethyl alcohol. To a few cc. of the acid solution add some crystals of sodium acetate and shake until they dissolve. Test this solution with a few drops of the indicator. The yellow color which develops is indicative of the almost complete suppression of the hydrogen ion due to the increased concentration of the acetate ion.
