Define the term base
Conjugate acid‐base pair = proton donor and the corresponding proton acceptor
Acid dissociation constant (Ka) equation
Keq = [A‐][H+]/ [AH]= Ka
Equation of pKa
pKa - -logKa
How do you determine pKa using the titration curve
When [AH] = [A‐], pH = pKa
(mid‐point of titration, half‐
neutralisation of the acid)
When [AH] < [A‐], pH > pKa
When [AH] > [A‐], pH < pKa
Buffers are required to stabilize pH
A buffer system consists of
A weak acid (proton donor) & its conjugate base (proton acceptor)
what does Isoelectric point (pI) mean
pH at which net charge on
a molecule is zero
How to find pl
0.5 (pKa1 and pKa2)
Henderson‐Hasselbalch equation
pH = pKa + log[(base/acid)]
How is the H-H equation used to prepare a
buffer?
- Some buffers supplied as free acid and corresponding base salt
- Need HH equation to calculate proportion of each at the desired pH
Steps to achieve a buffer
- 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
Fractional charge (FC)
FC = [charged]/([charged] + [uncharged])
