A buffer solution is made using a weak acid, HA. If the pH of the buffer is 1.0 × 101 and the ratio of A– to HA is 10, what is the pKa of HA?
Plug these numbers into the Henderson-Hasselbalch equation an solve for pKa.
To determine the pKa of HA, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Given that the pH is 1.0 × 10^1 and the ratio of [A-] to [HA] is 10, we can substitute these values into the equation:
1.0 × 10^1 = pKa + log(10)
Next, we can simplify the equation:
1.0 × 10^1 = pKa + 1
Now, we isolate pKa by subtracting 1 from both sides of the equation:
pKa = 1.0 × 10^1 - 1
Simplifying further:
pKa = 1.0 × 10
Therefore, the pKa of HA is 10.
To find the pKa of a weak acid, you need to know the pH and the ratio of the conjugate base (A-) to the acid (HA) in the buffer solution.
The pH is given in the question as 1.0 × 10^1 (which is 10). This value represents the concentration of H+ ions in the solution on a logarithmic scale.
In a buffer solution, the pH is determined by the equilibrium between the weak acid HA and its conjugate base A-. The Henderson-Hasselbalch equation describes the pH of a buffer solution:
pH = pKa + log ([A-]/[HA])
We are given that the ratio of [A-] to [HA] is 10, which means [A-]/[HA] = 10.
Substituting these values into the equation, we have:
10 = pKa + log (10)
To solve for pKa, we need to isolate it. Rearranging the equation:
pKa = 10 - log (10)
Using logarithmic properties, log (10) = 1:
pKa = 10 - 1
Therefore, the pKa of the weak acid HA is 9.