SIMPLE METHOD OF GRADING UNKNOWNS IN QUALITATIVE ANALYSIS' WALTER S. DYER Department of Chemistry, University of Arkansas, Fayetteville, Arkansas
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HE fact that qualitative analysis grades are The course as conducted in this laboratory includes twenty-four unknowns involving about 120 ions. The nature of the scheme of analysis causes thirteen of these unknowns to be of the simple type involving altogether not more than forty ions. Therefore, a t the rate of 100 points for each, a poor student might get a fairly good grade on over half the unknowns and thus offset a very bad grade on the others. A careful examination of the grades indicated that this was actually happening, whether intentionally or not, and that some students were getting grades which were out of proportion to their knowledge and to their care in the laboratory. In order to overcome the errors of this method it was decided to give no percentage grades until the end of the course. In the meantime the unknowns are scored as fractions. Thus an unknown containing five ions might be reported with four correct, one omitted, and one extra, which would merit a score of 4/6. The two figures are listed in vertical columns on the student's record sheet. At the end of the course the laboratory grade is something like 106/136, which may be given the value of 77.9 or 779. The latter value is used in this laboratory. Thus the entire laboratory portion of the course is made into a single project and the student receives a grade on his total achievement. A total of 169 students have been graded by this method and their grades were ranked as usual (A, B, C, D, F). For the sake of this study their grades according to the old method were also calculated and similar rankings were made. The proposed method gives a numerical grade spread which is more than ten per cent. greater than that attained by the old method in all the grade groups except the lowest. A considerable number of changes in rank were brought about by the new method of grading. Thus some were placed in the " A group who would not otherwise have been there and others were graded " F who would have passed had the old method been used. A careful consideration of the scores made on individual unknowns shows the continued efforts of those whose ranks were raised by this method. While this is not so evident in the cases of the better students it is markedly so with those in the lower-grade ranks. This method is quite satisfactory from the standpoint of the teacher as i t makes for simple calculation of grades and gives the better student credit for the ability to make a long and difficult analysis. In addition to this i t penalizes the careless and unwilling worker who uses little or no effort toward accuracy. * Research PaDer Number 437.. Tourual Series. Universitv of sometimes . unsatisfactory has been noted.'
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Arkansas. ' MARLOW,H. W., "Evaluatingunknownsinqualitativeanalysis," J. CAEM.EDUC.,11, 109-10 (Feb., 1934).
