a weak acid has a pKa of 6.0. what is the ratio of conjugate acid to conjugate base at pH 5?
Use the Henderson-Hasselbalch equation. Solve for (Base)/(acid)
To find the ratio of conjugate acid to conjugate base at a given pH, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log ([Conjugate base] / [Conjugate acid])
Given that the pKa of the weak acid is 6.0, we can substitute the values:
5 = 6.0 + log ([Conjugate base] / [Conjugate acid])
Rearranging the equation:
log ([Conjugate base] / [Conjugate acid]) = 5 - 6.0
log ([Conjugate base] / [Conjugate acid]) = -1.0
To get rid of the logarithm, we can rewrite the equation using exponential form:
[Conjugate base] / [Conjugate acid] = 10^(-1.0)
Now solving for the ratio:
[Conjugate base] = 10^(-1.0) * [Conjugate acid]
The ratio of the conjugate base to the conjugate acid is therefore given by 10^(-1.0), which is equal to 0.1.
To determine the ratio of conjugate acid (HA) to conjugate base (A-) at a specific pH, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Given that the pKa of the weak acid is 6.0 and we want to find the ratio at pH 5, we can rearrange the equation to solve for the ratio [A-]/[HA]:
[A-]/[HA] = 10^(pH - pKa)
Let's substitute the values into the equation to find the ratio:
[A-]/[HA] = 10^(5 - 6) = 10^(-1) = 0.1
Therefore, the ratio of conjugate acid (HA) to conjugate base (A-) at pH 5 is 0.1, or 1:10.