A buffer solution with a pH of 4.63 is prepared with 0.14 M formic acid and ________ M sodium formate. The K_a of formic acid is 1.8 × 10^-4. A)1.1 B)2.1 C)5.4 × 10^-6 D)3.0 × 10^-8 E)0.54

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Quizplus · Accepted Answer

The correct answer is A because the pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid. In this case, the pKa of formic acid is 1.8 × 10-4, and the pH of the buffer solution is 4.63. Therefore, log([A-]/[HA]) = 4.63 - 1.8 × 10-4 = 2.83. This means that the concentration of the conjugate base is 2.83 times greater than the concentration of the acid. Since the total concentration of the buffer solution is 0.14 M, the concentration of the conjugate base is 0.14 M / 2.83 = 0.05 M. Therefore, the concentration of sodium formate is 0.05 M.

A Buffer Solution with a PH of 4