According to Henderson-Hasselbach equation, if pH of a solution is less than pKa, then the amino acid consists of primarily of next most protenated form, where as when the pH of the solution is greater than the pKa, then the amino acids consists of primarily of next most deprotenated form. If the pH of the solution equals that of a pKa, then the amino acid consists of 50% of next most protenated and 50% of next most deprotenated form. The ionization of the amino acid wholly depends on the pH of the solution that they are dissolved in. Suppose the pH of solution was low (pH=1.0), then the amino acid is completely protenated and it has obtained a cationic form. As the pH increases, the carboxylic acid group ionizes first. When the pH equals pKa, the amino acids exist as a combination of protenated and the next most deprotenated form. This trend continues until all of the ionizable groups has been deprotenated. As the pH increases further, the amino group will lose a proton and ultimately, at a high pH (pH=12.0), the anionic form is the predominant form in solution. In certain amino acids, the R group ionizes depending on their polarity and the pKa value. In most cases, R group ionizes second after carboxyl group performs its complete ionization. In this experiment, a titration was performed for glycine and …show more content…
The carboxyl group has a net negative charge and the amino group a net positive charge. This is a zwitterionic form, where a positive and negative charge cancels out. When you raise the pH to well above the second pKa value (pH>9.60pKa), the nitrogen in the amino group will lose its proton and thus its charge. We now have negative charge on carboxyl group and a zero charge on amino group giving us a net negative one