The amino group can be protonated (that is, it has an extra proton attached) in a strongly acidic solution. This produces a diprotic acid of the form as exemplified by the protonated amino acid alanine. H2A+, as exemplified by the protonated amino acid alanine.

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Chapter14: Acids And Bases
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Problem 10RQ: For oxyacids, how does acid strength depend on a. the strength of the bond to the acidic hydrogen...
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7. Amino acids contain both an acidic carboxylic acid (-COOH) group and a basic amino group (-NH2).
The amino group can be protonated (that is, it has an extra proton attached) in a strongly acidic solution.
This produces a diprotic acid of the form as exemplified by the protonated amino acid alanine.
H2A+, as exemplified by the protonated amino acid alanine.
Protonated alanine
The protonated amino acid has two ionizable protons that can be titrated with OH".
OH
+H;NCHČOH
OH
+H,NCHCO
+ H,NCHČO
CH,
CH,
CH;
Protonated form
Neutral form
Anionic form
of alanine (H,A*)
of alanine (HA)
of alanine (A)
For the group, -COOH, pKa1,= 2.34, for the -NH", pK2 = 9.69
Consider the titration of a 0.500 M solution of alanine hydrochloride with 0.500 M NAOH solution. What is
the pH of
(a) the 0.500 M alanine hydrochloride;
(b) the solution at the first half-neutralization point;
(c) the solution at the first equivalence point?
The dominant form of alanine present at the first equivalence point is electrically neutral despite the
positive charge and negative charge it possesses. The point at which the neutral form is produced is
called the isoelectric point. Confirm that the pH at the isoelectric point is:
pH =(pK, + pKaz)
What is the pH of the solution:
(d) halfway between the first and second equivalence points? (e) at the second
equivalence point?
Transcribed Image Text:7. Amino acids contain both an acidic carboxylic acid (-COOH) group and a basic amino group (-NH2). The amino group can be protonated (that is, it has an extra proton attached) in a strongly acidic solution. This produces a diprotic acid of the form as exemplified by the protonated amino acid alanine. H2A+, as exemplified by the protonated amino acid alanine. Protonated alanine The protonated amino acid has two ionizable protons that can be titrated with OH". OH +H;NCHČOH OH +H,NCHCO + H,NCHČO CH, CH, CH; Protonated form Neutral form Anionic form of alanine (H,A*) of alanine (HA) of alanine (A) For the group, -COOH, pKa1,= 2.34, for the -NH", pK2 = 9.69 Consider the titration of a 0.500 M solution of alanine hydrochloride with 0.500 M NAOH solution. What is the pH of (a) the 0.500 M alanine hydrochloride; (b) the solution at the first half-neutralization point; (c) the solution at the first equivalence point? The dominant form of alanine present at the first equivalence point is electrically neutral despite the positive charge and negative charge it possesses. The point at which the neutral form is produced is called the isoelectric point. Confirm that the pH at the isoelectric point is: pH =(pK, + pKaz) What is the pH of the solution: (d) halfway between the first and second equivalence points? (e) at the second equivalence point?
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