A buffer is made by mixing $0.1$ M acetic acid ($pK_a = 4.74$) with $0.1$ M sodium acetate. The pH is:
A$4.74$, since $pH = pK_a + \log(1) = pK_a$ when ratio is 1
B$7.00$, since the solution is neutral with equal molarities
C$9.26$, since the buffer falls on the basic side here
D$0.00$, since acetate fully cancels the acid in the flask
Answer & Solution
Correct answer: A. $4.74$, since $pH = pK_a + \log(1) = pK_a$ when ratio is 1
Henderson-Hasselbalch: $pH = pK_a + \log([A^-]/[HA]) = 4.74 + 0 = 4.74$.
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