Lecture 5B

Question 1

Define the term base

Answer 1

Conjugate acid‐base pair = proton donor and the corresponding proton acceptor

Question 2

Acid dissociation constant (Ka) equation

Answer 2

Keq = [A‐][H+]/ [AH]= Ka

Question 3

Equation of pKa

Answer 3

pKa - -logKa

Question 4

How do you determine pKa using the titration curve

Answer 4

When [AH] = [A‐], pH = pKa
(mid‐point of titration, half‐
neutralisation of the acid)

When [AH] < [A‐], pH > pKa
When [AH] > [A‐], pH < pKa

Question 5

Buffers are required to stabilize pH

A buffer system consists of

Answer 5

A weak acid (proton donor) & its conjugate base (proton acceptor)

Question 6

what does Isoelectric point (pI) mean

Answer 6

pH at which net charge on

a molecule is zero

Question 7

How to find pl

Answer 7

0.5 (pKa1 and pKa2)

Question 8

Henderson‐Hasselbalch equation

Answer 8

pH = pKa + log[(base/acid)]

Question 9

How is the H-H equation used to prepare a

buffer?

Answer 9

• Some buffers supplied as free acid and corresponding base salt
• Need HH equation to calculate proportion of each at the desired pH

Question 10

Steps to achieve a buffer

Answer 10

• Determine ratio of acid and base
• Determine number of moles of each required
• Calculate mass of acid and base needed (use Mr)
• Weigh out correct mass, dissolve in beaker of dH2O
• Confirm pH
• Adjust to final volume

Question 11

Fractional charge (FC)

Answer 11

FC = [charged]/([charged] + [uncharged])