A student laboratory experiment has proved of value i n introducing the Lowy-Bronsted wiewpant on acids and bases to first-year students of general chemistry. Analogous titrations are carried out i n glacial acetic acid and i n aqueous solutions, end-points being determined by an indicator method.
I N A NUMBER of recent papers stress has beenlaid on the need for a modernization of first-year courses in general chemistry. Among the topics considered due for a revision are the fundamental conceptions of acids and bases (1, 2, 3, 4, 5). All authors agree that we should introduce the Lowry-Br@nsted ideas (6, 7) into our courses in an elementary way, redefining acids and bases in terms of their proton behavior. A simple and clear exposition of the modern view suitable for presentation to first-year students has recently beeu given by Dr. Kilpatrick (5).During the past .three years the writer has presented an elementary discussion of the newer ideas to his classes, introducing the subject shortly after a study of strong and weak electrolytes in which the electrical nature of ions and the dielectric behavior of the solvent is emphasized. Electronic explanations of salt formation have been given earlier in the year. I n spite of this background many students seemed to experience considerable difficulty in assimilating the newer ideas. When analyzed, the difficulty seemed to be due primarily to a complete unfamiliarity with solvents other than water, and to an inability to reconcile the older treatment as given in the textbooks with the modem conceptions. To the student the orthodox explanations of acid-base equilibria, hydrolysis, etc., seemed adequate in dealiig with the aqueous solutions to which his experience had been confined.To remedy this situation an experimental method of approach was devised whereby the student would have some actual experience with non-aqueous solutions. The work is adapted either to lecture demonstration or to student laboratory procedure. Because of its success with his classes, the writer prefers the latter.
THE LABORATORY MEHODThe experimental details are quite simple. Solutions of sodium acetate, potassium acetate, and perchloric acid in glacial acetic acid are prepared in the stockroom and are made available to the student. The sodium acetate and perchloric acid solutions are of known and approximately equivalent concentrations. Aqueous solutions of sodium hydroxide, potassium hydroxide, sodium acetate, and perchloric acid are also prepared so as to be equivalent in molality to each other and to the acetic acid solutions. As indicators, two 0.1% solutions of basic fuchsin are used, one in glacial acetic, the other in aqueous solution.The student is directed to titrate a 10-cc. portion of the solution of sodium acetate in acetic acid, using perchloric acid in the same solvent as the titrating acid. Two drops of indicator solution are used. He finds an endpoint when an equimolar quantity of the acid has beeu added; as the salt sodium perchlorate is soluble no precipitation occurs. He has b...