(a)
Interpretation:
The pH at which the zwitter ion [Z] and the cationic form [C+] of the amino acid alanine become equal needs to be calculated.
Concept introduction:
- Amino acids are organic compounds composed of C, H, N and O. The two main
functional groups include the amino −NH2 and carboxyl −COOH group in addition to a side chain each with a characteristic pKa value. - Isoelectric point (pI) is the pH at which the net charge on the amino acid is zero. For amino acid with one −COOH and one −NH2, the pI is given as:
Answer to Problem 30QAP
pH = 2.29
Explanation of Solution
The given amino acid is alanine which has the following structure:
The structures of the respective cationic form (C+), zwitter ion (Z) and the anionic form (A-) are:
The acid-base equilibria for alanine involving the cation and the zwitter ion forms is:
(b)
Interpretation:
The pH at which the zwitter ion [Z] and the anionic form [A-] of the amino acid alanine become equal needs to be calculated
Concept introduction:
- Amino acids are organic compounds composed of C, H, N and O. The two main functional groups include the amino −NH2 and carboxyl −COOH group in addition to a side chain each with a characteristic pKa value.
- Isoelectric point (pI) is the pH at which the net charge on the amino acid is zero. For amino acid with one −COOH and one −NH2, the pI is given as:
Answer to Problem 30QAP
pH = 9.74
Explanation of Solution
The given amino acid is alanine which has the following structure:
The structures of the respective cationic form (C+), zwitter ion (Z) and the anionic form (A-) are:
The acid-base equilibria for alanine involving the anion and the zwitter ion forms is:
(c)
Interpretation:
The pH at the isoelectric point needs to be calculated
Concept introduction:
- Amino acids are organic compounds composed of C, H, N and O. The two main functional groups include the amino −NH2 and carboxyl −COOH group in addition to a side chain each with a characteristic pKa value.
- Isoelectric point (pI) is the pH at which the net charge on the amino acid is zero. For amino acid with one −COOH and one −NH2, the pI is given as:
Answer to Problem 30QAP
pH = 6.02
Explanation of Solution
For alanine at the isoelectric point:
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Chapter 23 Solutions
Chemistry: Principles and Reactions
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