Chapter 9 - Polyprotic Acids-Bases Equilibria

Question 1

Polyprotic acid ____ in successive steps with it’s own _____

• ____ is the acid ionization for the first steps, _____ is the base ionization first step
• ____ is the acid ionization for the second steps, _____ is the base ionization second step

Answer 1

ionize, Ka

• Ka1, Kb2
• Ka2, Kb1

Question 2

Diprotic acids
When polyprotic acids disassociate, multiple forms of ____ ____ are present

what is a good example of diprotic acids?

Answer 2

initial species

amino acids

Question 3

Amino acids

Non-ionized forms rearrange into _____
- Both ___ and ___ sites

Answer 3

zwetterions

- positive and negative

Question 4

Diprotic acids:

Acidic form =
- approximation Ka = __ and Ka2 = __

Basic form =
- Kb = __ and Kb2 = __

Intermediate form =
- intermediate for is ____

The pH of the intermediate form of diportic acid is close the midway between ___ and ____, regardless of formal charge.

Answer 4

cation
- Ka1, neligible

anion
- Kb1, neligible

amophteric

pka1, pka2

Question 5

Principles Species

Describe the distrubtion of analyte among possible species.
- how can you know what species are present?

Answer 5

Speciation

- pKa’s

Question 6

Speciation: Monoprotic - what’s present? (HA)

1. pH < pKa
2. pH > pka
3. pH = pka

Answer 6

1. HA present
2. A- present
3. 1:1 mixture

Question 7

Speciation: Diprotic (H2A)

1. pH < pKa1:
2. pKa1 < pH < pKa2:
3. pKa2 < pH:
4. pH = pKa1:
5. pH = pKa2:

Answer 7

1. H2A present
2. HA- present intermediate
3. A2- present
4. 1:1 mixture of H2A and HA-
5. 1:1 mixture of HA- and A2-

Question 8

Speciation: Triprotic (H3A)

1. pH < pKa1: Acidic H3A is present
2. pKa1 < pH < pKa2: Intermediate H2A- is present
3. pKa2 < pH < pKa3: Intermediate HA2- is present
4. pKa3 < pH: Basic A3- is present
5. pH = pKa1: 1:1 mixture of H3A and H2A-
6. pH = pKa2: 1:1 mixture of H2A- and HA2-
7. pH = pKa3: 1:1 mixture of HA2- and A3-

Answer 8

1. H3A present
2. H2A- present
3. HA2- present
4. A3- is present
5. 1:1 mixture of H3A and H2A-
6. 1:1 mixture H2A- and HA2-
7. 1:1 mixture HA2- and A3-

Question 9

When does fractional compostion occurs?

Answer 9

pH = pKa

Question 10

Isoelectric and Isoionic pH:

The pH obtained when the pure, neutral polyprotic acid HA is dissolved in water. 
Only ions are:
H2A+
A-
H+
OH-

Answer 10

Isoionic point

Question 11

The pH at which the average charge of the polyprotic acid is zero.

• Most of the molecules are in the uncharged form HA.
  
  • [H2A+] = [A-]

Answer 11

Isoelectric point