Produce a reading outline for the chapter on amino acids and the section that introduces the peptide bond. Commit to memory the structures of the amino acids.

Organic Chemistry: A Guided Inquiry
2nd Edition
ISBN:9780618974122
Author:Andrei Straumanis
Publisher:Andrei Straumanis
Chapter27: Amines
Section: Chapter Questions
Problem 12CTQ
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1. Produce a reading outline for the chapter on amino acids and the section that introduces the peptide
bond. Commit to memory the structures of the amino acids.
2. Draw a titration curve for the amino acid lysine using the pK s of 2.2, 9.0 and 10.0 for the ionizable
groups of lysine. Use the titration curve in Model 1 and its description as a model for your drawing.
Label the buffering regions and equivalence points. Draw the structures for the primary species of
lysine at all the buffering regions and equivalence points you include in your graph. You might find it
helpful to answer questions 1 and 2 to complete this.
3. Define the term buffering region and describe how you could locate the buffering region on a titration
curve.
4. Define the term equivalence point and describe how you could locate the equivalence point on a
titration curve.
Model Titration Curve
The graph below is a titration curve in which a solution of NaOH is added to a solution of
propanoic
acid (HPr). (This type of titration is often covered in general chemistry.) At pointA the primary form
present is the conjugate acid (HPr). As OH- is added,
it forms water by combining with protons in the
solution. This reduces the concentration of HPr and
Model 1 Titration of propanoic acid with
NAOH
produces the conjugate base propionate (Pr-). The
Ka for propanoic acid is 1.3 x 10-5 and the pK, for
propanoic acid is 4.89. When the pH of a solution of
HPr is 4.89 (the pH equals the pK, which is point B
on the graph), the concentration of the conjugate acid,
HPr, and the concentration of the conjugate base Pr-
are equal. For acids and bases, it is always true that
the concentrations of the respective conjugate acid/
base pair are equal when the pH is equal to the pK, of
the conjugate acid. This is usually called the buffering
region. Point C on the graph is the equivalence point.
At this point the molar amount of monoprotic acid in
the original solution is equal to the molar amount of
OH- added, i.e. the equivalents of protons equals the
equivalents of base added.
14
12
10
8.
6.
4
0.5
1.0
Equivalents of NaOH added
3.
B.
Hd
Transcribed Image Text:1. Produce a reading outline for the chapter on amino acids and the section that introduces the peptide bond. Commit to memory the structures of the amino acids. 2. Draw a titration curve for the amino acid lysine using the pK s of 2.2, 9.0 and 10.0 for the ionizable groups of lysine. Use the titration curve in Model 1 and its description as a model for your drawing. Label the buffering regions and equivalence points. Draw the structures for the primary species of lysine at all the buffering regions and equivalence points you include in your graph. You might find it helpful to answer questions 1 and 2 to complete this. 3. Define the term buffering region and describe how you could locate the buffering region on a titration curve. 4. Define the term equivalence point and describe how you could locate the equivalence point on a titration curve. Model Titration Curve The graph below is a titration curve in which a solution of NaOH is added to a solution of propanoic acid (HPr). (This type of titration is often covered in general chemistry.) At pointA the primary form present is the conjugate acid (HPr). As OH- is added, it forms water by combining with protons in the solution. This reduces the concentration of HPr and Model 1 Titration of propanoic acid with NAOH produces the conjugate base propionate (Pr-). The Ka for propanoic acid is 1.3 x 10-5 and the pK, for propanoic acid is 4.89. When the pH of a solution of HPr is 4.89 (the pH equals the pK, which is point B on the graph), the concentration of the conjugate acid, HPr, and the concentration of the conjugate base Pr- are equal. For acids and bases, it is always true that the concentrations of the respective conjugate acid/ base pair are equal when the pH is equal to the pK, of the conjugate acid. This is usually called the buffering region. Point C on the graph is the equivalence point. At this point the molar amount of monoprotic acid in the original solution is equal to the molar amount of OH- added, i.e. the equivalents of protons equals the equivalents of base added. 14 12 10 8. 6. 4 0.5 1.0 Equivalents of NaOH added 3. B. Hd
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