BCHM 218 Lecture Notes - Lecture 1: Titration Curve, Zwitterion, Acid Dissociation Constant
2 Jun 2020
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Document Summary
Pka. the ph at which on average half of the molecules of that species are deprotonated. The pka for the carboxyl group is usually 2. The pka for the amino group is usually b/w 9-10. Aas with an ionizable side chain will usually have 3 pka values. At very acidic ph values, aas tend to be positively charged. At alkaline ph values, aas tend to be negatively charged. At low ph values -> glycine has a positive charge and is fully protonated. The concentration of the fully protonated glycine is equal the he concentration of the zwitterion. Here ph is close to the pka value: The solution = buffer; titration curve = somewhat flat. Addition of more base means carboxylate group transitions from being half-protonated to fully deprotonated! Here, we have the aa stops acting like a buffer and ph rapidly increasing. Once we have added a total of 1. 0 equiv of base.
