SHOULD QUANTITATIVE ANALYSIS BE TAUGHT befre QUALITATIVE ANALYSIS? LYLE 0. HILL
AND
WILLIAM F. CRAMER
Central Y. M. C. A. College, Chicago, Illinois
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ROBABLY the most difficulttask in the teaching of college chemistry is the coordination of the laboratory work and the theoretical material which is covered in the course in qualitative analysis. Practically all teachers admit that this is desirable and strive for this coordination; however, very few have been satisfied with their results. The laboratory work in the first part of the course is mainly cookbook in style. Usually the end of the course is reached before the student begins to see the relation between the laboratory work and the material discussed in the lecture room. Several times we have tried rearranging the material which is most essential for the qualitative course in such a way as to make a better coordination between the laboratory work and the lecture material.
Our results have not been all that could be desired, however. When we follow the logical order for an ultimate analysis, are we following the most effective method of presenting this fundamental material to our students? Or should we reverse our present order and make introductory quantitative analysis a prerequisite for qualitative analysis? Since the chemistry involved in the analysis of the unknowns usually used in the first quantitative course is so much simpler than that encountered in the qualitative scheme the authors believe that this rearrangement will be preferable in obtaining the objectives of these courses. Before proceeding further, we might outline the more important objectives of a qualitative and a quantitative course.
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(1) Create scientific interest. The application of quantitative work to nearly all types of commercial work, as well as all phases of chemistry, is easily pointed out by the instructor. This gives the students a feeling that they are doing chemical work rather than preparing to do it. (2) A working knowledge of solutions of electrolytes. (3) The development of manipulative skill in the laboratory. (4) An appreciation of the application of theories and laws to the practical laboratory work. The long delay in bringing out the fourth objective in the course in qualitative analysis is the problem with which we are confronted. If quantitative analysis were taught before qualitative analysis the student entering the qualitative course would have sufficient background t o avoid the delay in conrdinating the laboratory work and the theoretical material. Would there be a similar delay in the quantitative course? By use of the following order it is believed that no such delay would occur. (1) An introductory discussion of the use of the quantitative apparatus. (2) A discussion of stoichiometry of acids and bases which brings out the practical application of the atomic theory. There is no logical place to bring in this discussion in the qualitative course, although it is needed before the introduction of the mass law, since most students do not get a sufficient background in their general chemistry. (3) The application of the mass law and hydrolysis to acidimetry and alkalimetry. The titration of acetic acid. The choice of an indicator in the titration of a weak electrolyte shows the practical application of the mass law in a much more simple and more fundamental manner than is shown a t any place in the qualitative scheme. (4) The stoichiometry of oxidation-reduction reaction shows much more forcibly the need for the ability to balance oxidation-reduction equations than any reason that can be given in connection with the qualitative scheme. Also, the reactions involved in the determination of iron or copper are much more simple than those reactions encountered with the copper-arsenic group of the hydrogen sulfide scheme. (5) The application of the solubility product law to gravimetric work brings out a number of very interesting practical examples such as the amount of precipitate that will dissolve in the wash solution and the effect of the common ion in loss of the precipitate due to solution.
(6) Coprecipitation. A little knowledge of this phenomenon should be an asset when discussing the qualitative scheme. However, it is usually not considered until the quantitative course.
If the student entering qualitative analysis has studied the material outlined above, only a short time would be required to study the application of the mass law to complex ions and to discuss amphoteric compounds. Then a student would be ready for a complete breakdown and study of the qualitative scheme, based on the above theories and laws, which could proceed along with the work in the laboratory. Two of the objections to this suggested order are:
(1) The logical order of an analysis is a qualitative analysis and then a quantitative analysis, which is probably the reason for the order now in use. Chemistry, however, has developed so that i t is very seldom necessary for a chemist to run a qualitative analysis. (2) The technic acquired in the qualitative laboratory work aids the quantitative work. This is no doubt true, but is it necessary? Would not the technic acquired in quantitative be more valuable in doing qualitative work? There are a few administrative problems that will arise with this order. More time will have to be scheduled for the lecture work in the quantitative course, and, therefore, less laboratory work required, or the credit hours increased. Would the quantitative course as outlined meet the entrance requirements of certain professional schools, particularly pharmacy where only one analytical course is expected? At the present time we are considering the adoption of this plan in either the spring or the faU of 1939 a t the Central Y. M. C. A. College. Before we make such a move, however, we would like to have the opinions and suggestions of others interested in teaching these two courses. Needless to say, we expect t o keep complete records so that the progress of students taking quantitative analysis first can be compared with that of students taking qualitative analysis first. We have a t our disposal rather complete records on each of our students. Using these we shall study our results by the method of equated groups. Criteria for match'mg the experimental and control groups will be (1) general ability as determined by a psychological examination; (2) general scholarship asmeasured by college marks; and (3) marks in general chemistry.
