(a) Glycine is present predominantly as the species “HaN-CH2-COOH. (b) The average net charge of glycine is +1/2. c) Half of the amino groups are ionized. (d) The pH is equal to the pka of the carboxyl group. (e) The pH is equal to the pka of the protonated amino group. (f) Glycine has its maximum buffering capacity. (g) The average net charge of glycine is zero. (h) The carboxyl group has been completely titrated (first equivalence point). (i) Glycine is completely titrated (second equivalence point). G) The predominant species is *HaN-CH2-COO (k) The average net charge of glycine is 21. (1) Glycine is present predominantly as a 50:50 mixture of “H&N-CH2-COOH and “H3N-CH2-CO0 (m) This is the isoelectric point.
(a) Glycine is present predominantly as the species “H3N-CH2-COOH.
(b) The average net charge of glycine is +1/2.
(c) Half of the amino groups are ionized.
(d) The pH is equal to the pka of the carboxyl group.
(e) The pH is equal to the pka of the protonated amino group.
(f) Glycine has its maximum buffering capacity.
(g) The average net charge of glycine is zero.
(h) The carboxyl group has been completely titrated (first equivalence point).
(i) Glycine is completely titrated (second equivalence point).
(j) The predominant species is “H3N-CH2-COO
(k) The average net charge of glycine is 21.
(1) Glycine is present predominantly as a 50:50 mixture of “HsN-CH2-COOH and “HN-CH2-COO
(m) This is the isoelectric point.
(n) This is the end of the titration.
(o) These are the worst pH regions for buffering power.
The Correct Answer and Explanation is :
Let’s break down the situation described and the options provided, based on the typical titration curve of glycine, an amino acid.
(a) Glycine is present predominantly as the species “H3N-CH2-COOH.”
This statement is true at a low pH. At low pH, the amino group (-NH2) will be protonated to form -NH3+, and the carboxyl group (-COOH) will remain in its neutral form. Therefore, glycine predominantly exists as “H3N-CH2-COOH” in acidic conditions.
(b) The average net charge of glycine is +1/2.
This is likely incorrect because the net charge of glycine at any given pH is an integer value, not a fraction.
(c) Half of the amino groups are ionized.
This statement is true at the pKa of the amino group (about 9.6), where half of the amino groups will be protonated (-NH3+) and the other half will be neutral (-NH2). This corresponds to the buffering region for the amino group.
(d) The pH is equal to the pKa of the carboxyl group.
This statement is true at the pKa of the carboxyl group (about 2.34). At this pH, half of the carboxyl groups will be protonated (-COOH) and the other half will be deprotonated (-COO-).
(e) The pH is equal to the pKa of the protonated amino group.
This is true at the pKa of the protonated amino group, which is approximately 9.6. At this point, glycine exists as a mix of neutral and protonated species.
(f) Glycine has its maximum buffering capacity.
This statement is true at the pH near the pKa values, where the buffering capacity of an amino acid is most effective.
(g) The average net charge of glycine is zero.
This is true at the isoelectric point (pI), which is around pH 5.97 for glycine. At this pH, the amino and carboxyl groups are in a state where their charges cancel each other out.
(h) The carboxyl group has been completely titrated (first equivalence point).
This is true at pH 2.34, when the carboxyl group (-COOH) has lost its proton, forming -COO-.
(i) Glycine is completely titrated (second equivalence point).
This occurs at pH 9.6, when the amino group (-NH3+) loses its proton, forming -NH2.
(j) The predominant species is “H3N-CH2-COO.”
This is true at basic pH, above the pKa of the amino group, where the amino group is deprotonated (-NH2) and the carboxyl group is deprotonated (-COO-).
(k) The average net charge of glycine is +1.
This is true in acidic conditions when the amino group is protonated and the carboxyl group is neutral.
(l) Glycine is present predominantly as a 50:50 mixture of “H3N-CH2-COOH and “H3N-CH2-COO.”
This is true at the pI, where both the carboxyl and amino groups are in equilibrium between their protonated and deprotonated forms.
(m) This is the isoelectric point.
This is true when the net charge of glycine is zero, typically occurring at pH 5.97.
(n) This is the end of the titration.
The end of the titration occurs when all titrable groups have been deprotonated or protonated, i.e., at the second equivalence point (pH 9.6).
(o) These are the worst pH regions for buffering power.
This is true at extreme pH values far from the pKa values, where the buffering capacity of glycine is minimal. This occurs at very low or very high pH, beyond the buffering range of the carboxyl and amino groups.
Correct Answers:
- (a) Glycine is present predominantly as the species “H3N-CH2-COOH.”
- (c) Half of the amino groups are ionized.
- (d) The pH is equal to the pKa of the carboxyl group.
- (e) The pH is equal to the pKa of the protonated amino group.
- (f) Glycine has its maximum buffering capacity.
- (g) The average net charge of glycine is zero.
- (h) The carboxyl group has been completely titrated (first equivalence point).
- (i) Glycine is completely titrated (second equivalence point).
- (j) The predominant species is “H3N-CH2-COO.”
- (l) Glycine is present predominantly as a 50:50 mixture of “H3N-CH2-COOH and “H3N-CH2-COO.”
- (m) This is the isoelectric point.