are also used to further assess the students’ analytical skills. In
these experiments all students generally determine the unknown
concentration to within 5% of the expected value. These results
indicate that students benefit from the opportunity the experiment
provides to learn about a critical analytical tool.
In the second part of the experiment, the method of
continuous variation ( Job’s method) is used to investigate
the stoichiometry of the iron–salicylate coordination complex
formed. Varying volumes of 10 mM solutions of sodium
salicylate and iron(III) nitrate are mixed and diluted to prepare
eleven test solutions (see Table 1 in the online material). The
total combined volume of the two solutions remains constant
(1 mL), and thus only the mole ratio of iron to salicylate changes
in these solutions. The test solution that exhibits the largest
absorbance at λmax indicates the mole ratio of the predominant
complex formed in the reaction. This maximum is most easily
demonstrated in a plot of absorbance versus mole fraction of
iron(III).