Week 3: Acid-base Properties Of Amino Acids

Question 1

What is the Brønsted-Lowry definition of acids?

Answer 1

Acids are proton (H+) donors

Example: HA → H+ + A-

Question 2

What is the Brønsted-Lowry definition of bases?

Answer 2

Bases are proton (H+) acceptors

Example: B + H+ → BH+

Question 3

What is the acid dissociation constant (K_a)?

Answer 3

K_a = [H+] × [A-] / [HA]

pK_a = -log K_a

Question 4

What does a lower pK_a indicate about an acid?

Answer 4

The stronger the acid

Stronger acids have higher K_a values than weaker acids.

Question 5

What is the relationship between strong acids and their conjugate bases?

Answer 5

The stronger the acid HA, the weaker the conjugate base A-

Question 6

What is a buffer solution?

Answer 6

A buffer solution tends to resist pH changes when small amounts of acid or base are added.

Question 7

What are buffers made of?

Answer 7

Mixtures of weak acids and their conjugate bases.

Question 8

What is the buffering region?

Answer 8

pK_a +/- 1 pH unit

Question 9

What is the isoelectric point (pI)?

Answer 9

pI = (pK_1 + pK_2)/2

pI is the pH at which net charge is zero.

Question 10

What happens to the ionization state of amino acids with varying pH?

Answer 10

The ionization state of amino acids varies with the pH.

Question 11

What is the pK_a of acetic acid?

Answer 11

4.76

Question 12

What occurs at pH 3 for acetic acid?

Answer 12

Mostly protonated (CH3COOH)

Question 13

What occurs at pH 6 for acetic acid?

Answer 13

Mostly deprotonated (CH3COO-)

Question 14

Fill in the blank: Acids are proton (H+) _______.

Answer 14

donors

Question 15

Fill in the blank: Bases are proton (H+) _______.

Answer 15

acceptors

Question 16

What is the significance of titration curves in amino acids?

Answer 16

They can be used to determine the pK_a, isoelectric point (pI), and buffer regions of an amino acid.

Question 17

True or False: The stronger the base B, the weaker the conjugate acid BH+.

Answer 17

True

Question 18

What is the formula used to calculate the acid dissociation constant K_a?

Answer 18

K_a = [H+] × [A-] / [HA]

Question 19

What does the ionizable groups in amino acids refer to?

Answer 19

Amino acids can act as acids and bases (amino group and carboxyl group).

Question 20

What is the relationship between [CH3COOH] and [CH3COO-] at pK_a?

Answer 20

[CH3COOH] = [CH3COO-]

This is when K_a = [H+] × [CH3COO-] / [CH3COOH].

Question 21

What does a titration curve of an amino acid show?

Answer 21

The net charge of the amino acid at different pH levels.