A Project-Type General Chemistry Experiment Recently the concept of using project-type freshman laboratory experiments has become of great interest. One of the most complete was done by Splittgerber, Maclean, and Neils.' The following experiment was designed to follow the project approach and could be used effectively as s second semester freshman laboratory experiment or in a quantitative analysis course. The project includes the synthesis and analysis of the inorganic complex [Co(NHdCIICL. The students were told that the possible substituents involved could include Co3+, NH3, C1-, and HzO. Their long term god was to analyze a compound they had prepared and determine its formula, the %yield and the K,,. The following analyses were carried out. Analysis of Chloride. The students prepared an AgN03 solution which was standardized by the Mohr and Fajan method against primary standard NaCl solid to illustrate different types of end point equilibrium. The standard AgN03 was then used to standardize KSCN for use in the Volhard determination of the tatal chloride. Separation of the ionic chloride was carried out on a strong acid ion exchange column such as Dowex 50W-X8. A very small column sufficed to carry out the separation. The eluted liquid was analyzed for ionic chloride by the Fajan method. Analysis for N H 3 The analysis for NHs was carried out by a Kjeldahl decomposition followed by hack titrating the standardized acid that was used in the receiver flask with standardized NaOH. Standardization of the acid was carried out by titrating- against primary standard sodium carbonate. The base was standardized by means of a potentiametric titration. Analysis of Cobalt. For this determination it was decided to use a spectraphatometric method. A sample of the complex was dissolved and reacted with Nitrosa-R-Salt which produces another soluble complex of a different color. Each student prepared a standard curve of concentration versus absorbance, and by the comparison of spectroscopic readings of their sample t o the standard curve they determined the concentration of their unknown. If equipment was not available to do this determination spectmscopically, the cobalt could he analyzed by a gravimetric method of destroying the complex with concentrated H ~ S O I - H N Oand ~ fuming off the excess acids leaving CoSO,. Analysis of HzO. This was determined by percent total difference. Determination of K I P . The individual students devised their awn methods for this determination. Methods used were analysis of total chloride, analysis of ionic chloride, base titrations of the Hi released from the column during exchange, NHI analysis and spectrometric determinations. A detailed set of directions may be obtained by writing Mr. Vernon Tbielmann, Chemistry Department, Baylor University, Waco. Texas 76703. ~
Splittgerber, A. G., MacLean, D. B.. and Neils. J., J. CHEM. EDUC., 48,330 (1971) Baylor University Waeo, Texas
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Journal of Chemical Education
Vernon Thielmann
