Solubility of Lead Chloride: Common Ion and Complexation Effects in a Greener Laboratory Experiment

Lead chloride has a moderate solubility, allowing small, but quantifiable, amounts to be used in a lab experiment studying solubility. Two gravimetric methods are compared by each student. The first method involves weighing excess lead chloride before and after dissolution. The second method precipitates dissolved lead ion from a saturated solution. The most common error in both methods, not collecting all of the solid, results in high solubility values in the first method and low solubility values in the second. This can lead to rich student discussion and evaluation of these techniques. Using sulfate as the precipitating agent is greener than using chromate as the precipitating agent; similar results are obtained, and the importance of green chemistry can be introduced. To further enrich the chemistry content exploration in this lab experiment, each student measures solubility in a different sodium chloride concentration, leading to observable common ion and complexation effects. This laboratory experiment is done in one 3 h lab period in an analytical chemistry course that has a heavy emphasis on chemical equilibria and is followed up by additional calculations later in the course.