What is the percentage of a weak acid (pka = 5.4) in the non-ionized form in plasma (ph 7.4)?

0.99%

Explanation:

The Henderson-Hasselbalch equation relates the ratio of the ionized to the non-ionized form of an acid as follows:

pH = pKa + log([A⁻]/[HA])

Inserting the values for pH and pKa and solving gives:

7.4 = 5.2 + log([A⁻]/[HA])

2 = log([A⁻]/[HA])

[A⁻]/[HA] = 100/1

The percentage of the weak acid in non-ionized form (HA) is then calculated:

[HA]/([A⁻] + [HA]) = 1/(100+1) x 100% = 0.99&