Friday, January 20, 2006

Lecture Summary 1/20: A new look at old chemistry - Lewis acids and bases

Noticing patterns among reactions is helpful in both predicting the results of novel reactions and in explaining the results of new reactions. One set of common patters includes ionic precipitation reactions, Lewis acid/base reactions and oxidation-reduction reactions. We reviewed the solubility rules very briefly, did an quantitative example based on the precipitation of lead by sulfate to improve the qualilty of drinking water for workers in lead paint factories. The Lewis acid-base framework extends the definition of Bronsted and Lowry of acids and bases. Lewis acids are electron pair acceptors, Lewis bases are electron pair donors. Examples of reactions that the framework covers includes: proton transfer reactions (such as the reaction of HCl with water), metal-ligand binding (example of cisplatin and EDTA) and nucleophile/electrophile (such as the ninhydrin reaction to detect fingerprints). Different acids have different strengths, as we noted in the EDTA binding example.

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