INTRODUCING ORGANIC CHEMISTRY in the LABORATORY* JOHN B. ENTRIKIN Centenary College of Louisiana, Shreveport, Louisiana
B y introducing the work in the organic chemistry medical and other students not majoring in chemistry. laboratory with a series of pantitatiwe experiments reThe following type of experiment i s suggested for the lated to the laboratory work in inorganic chemistry, and first few laboratory periods: qwllitatine analysis for the yet of a definite organic chemical significance, one furnishes elements C. S, N, and the halogens; titration experithe student a natural bridge between the two courses. ments designed to study indicators, salt hydrolysis, buffer For those who haue not had quantitative analysis, the action, and pH; and the determination of the percentage training i s conducine to precise work throughout the of nitrogen in organic unknowns by both the macroyear. The course is particularly valuable to pre- Kjeldahl and the micro- (colorimetric) methods.
+ + + + + + HE average textbook written for the student who is taking up the study of organic chemistry offers very little material during the fmt weeks of study out of which practical laboratory experiments may be developed. This problem has been met by most writers of laboratory guides by introducing the student in the laboratory to the methods of purifying organic compounds, and to the determi-
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"Presented before the Division of Chemical Education of the A. C. S. at Denver, Colorado. August 23, 1932.
nation of the physical constants of representative compounds. I t seems to the writer that purification methods might better be taken up in connection with actual preparation experiments where the student has the "setting" for the need and the adaptability of the method to be employed. The same argument, it seems, would apply ~hysical .. . to the determination of . constants. AN too frequently, the student who is beginning
the study of organic chemistry feels that it is entirely different from inorganic chemistry, and that he need not recall or remember the principles and facts which he learned in the previous course. A large number, perhaps even a majority, of the students who register for organic chemistry have not previously taken work in quantitative analysis. Furthermore, the majority of those who have not already taken the quantitative work will not take it a t all. The discussion on premedical education in chemistry at the A. C. S. meeting in New Orleans last spring brought out the fact that the majority of those present felt that more quantitative work should he introduced into the laboratory practice in orgauic chemistry for premedical students. Quantitative experiments serve several functions. In the iirst place, the ordinary organic laboratory work is too frequently pursued in a careless manner. The type of experiment suggested to the students allows them to anticipate or calculate the results that should be obtained, and the temptation is very great to get those results. Experiments should be given, particularly during the first few periods, which do not allow these possibilities. Secondly, certain quantitative experiments may be used to act as a natural bridge between inorganic and organic chemistry. Furthermore, the student is made to feel the need of painstaking work which will result in data acceptable to the instructor. The student is made to realize the need for carefully planning his work in order that precision may be attained. The attitude thus created toward the laboratory work will, in the writer's opinion, last to a considerable degree throughout the year. A certain zest is added to the work of the student if the experiment involves the determination of an "unknown." Such experiments have not been common in the manuals for organic chemistry. This type of experiment is well adapted to the determination of the aptitude, technic, and knowledge of the student. Considering these views, the writer has tried the following series of experiments as the introduction to the year's work in the organic laboratory, and has been pleased with the results:
I. Methods for the qualitative detection of C, CI, Br, I, S, and N. Two individual "unknowns" are run after the satisfactory completion of the practice work. 11. The titration of 0.1 N HC1 with approximately 0.1 N NaOH. The standard acid is prepared by the students by diluting "constant-boiling" HC1 which they have previously prepared as an experiment in fractional distillation. The alkali solution is prepared by the students by diluting 45% NaOH which has stood to allow the precipitation of NaHCOa. Three Merent indicators are used, and a study is made of the indicator endpoints, equivalent points, and the neutral point. 111. Salt hydrolysis, and the buffer action of salts. Titration data are obtained and interpreted for the followingreactions, both methyl orange and phenolphthalein being used as indicators:
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1. HCI NazC01 2. HC1 NaOH (NaHC03being present) 3. HC1 NaOH (NHSI being present) 4. HaPo, NaOH The use of a color comparator set for the determination of the pH of a solution is thoroughly explained and demonstrated. The pH values of solutions of salts like those produced by the above readions are determined by the students, and the relationship of the pH of the solution of the salt to the pH range of the proper indicator far the reaction is pointed out. IV. Determination of a nitrogen "unknown" by the macroKjeldahl method. The standard solutions of acid and base previously prepared are used. V. Determination of a nitrogen "unknown" by the micromethod, using the calorimeter.
After an introduction to organic chemistry laboratow , oractice bv means of these exoeriments involvine such organic compounds as carbonates, cyanides, indicators, and organic nitrogen compounds, our students proceed to a study of the solubilities and class reactions of representative members of the principal classes of carbon compounds. A reasonable number of compounds is prepared, purified, and the percentage yield calculated. These preparations are selected to teach general principles of carbon chemistry, such as the methods of replacing the -OH group by a halogen atom. Unknowns are given the students to determine the class to which they belong, based on solubility data, the elements present, and chemical reactivity. Both qualitative and quantitative unknowns are given the students during the studies involving the sugars. &
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