The precision of scientific apparatus has direct implication on the accuracy of the measured results. This can be characterized by propagation of error and statistics. An experiment to measure the molar extinction coefficient of a compound was developed to illustrate this effect. Students were instructed to make two sets of solutions, one set using volumetric flasks and pipets and the other set using only beakers. The students calculated the uncertainty in the concentration measures by propagating the error due to the tolerances of the glassware. The series of measured absorbances for each set was used to calculate the extinction coefficient of copper(II) ammonium chloride, Cu(NH3)4Cl2 , and its uncertainty. Cu(NH3)4Cl2 was used due to the ready availability of copper (II) chloride in the laboratory. The use of CuCl2 led to some issues which will be discussed and alternative materials will be suggested. Students were able to clearly see the effects of glassware tolerance on their results.

Solution concentration uncertainty: An experiment to illustrate the concepts of precision and propagation of error through measurement of the molar extinction coefficient of Cu(NH3)4Cl2

249th National Meeting (2015)

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