QQuestionChemistry
QuestionChemistry
A buffer solution at pH 10 has a ratio of [HA]/[A-] of 10. What is the pKa of the acid?
A. 8
B. 9
C. 10
D. 11
E. 12
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Answer
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Step 1:Let's solve this step by step:
Step 2:: Recall the Henderson-Hasselbalch equation
pH = pK_a + \log\frac{[A^{-}]}{[HA]}
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of conjugate acid and base concentrations:
Step 3:: Rearrange the given information
We know: - pH = 10 - Ratio of [HA]/[A^{-}] = 10 - We want to find pKa
Step 4:: Rearrange the Henderson-Hasselbalch equation
10 = pK_a + \log\frac{1}{10}
First, note that the ratio given is [HA]/[A^{-}], which is the inverse of the ratio in the equation.
Step 5:: Solve for pKa
pK_a = 11
10 = pK_a - 1
Step 6:: Verify the solution
- pH = 11 (pKa) - log(2$) = - 1 - [HA]/[A^{-}] = 10 ✓
Final Answer
The pKa of the acid is 11.
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