7. At pH 7.4 a weak organic acid with a pKa of 6.4 would be ionized at what percent?
To determine the percent ionization of a weak acid at a certain pH, you need to consider the acid dissociation constant (Ka) and the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log ([A-]/[HA])
Where:
- pH is the given pH value
- pKa is the acid dissociation constant of the weak acid
- [A-] is the concentration of the ionized form of the acid
- [HA] is the concentration of the non-ionized form of the acid
In this case, you are given the pH as 7.4 and the pKa as 6.4. We can rearrange the Henderson-Hasselbalch equation to solve for the percent ionization:
[A-]/[HA] = 10^(pH - pKa)
Substituting the given values:
[A-]/[HA] = 10^(7.4 - 6.4)
[A-]/[HA] = 10^(1)
[A-]/[HA] = 10
The ratio [A-]/[HA] represents the percent ionization. Therefore, at pH 7.4, the weak organic acid with a pKa of 6.4 would be ionized at 10%.