What is the calculated pH of a buffer solution prepared by mixing 0.1 M ethanoic acid (acetic acid, pKa = 4.76) with 0.1 M sodium ethanoate (sodium acetate) at 298 K?
Answer and explanation
Correct answer: D. 4.76
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.
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- Step 1: Apply the Henderson-Hasselbalch equation for an acidic buffer:
- Step 2: Here, , and .
- Step 3: .
- Step 4: Since :
- Step 5: When the concentrations of weak acid and conjugate salt are equimolar, the buffer capacity is maximum and .
Answer
4.76
Why not the others: '7.00' represents a neutral solution; '9.24' is ; '3.76' assumes a 10-fold excess of acid.
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