Calculate the pH of a solution that is 0.278 M in sodium formate (NaHCO₂)and 0.222 M in formic acid (HCO₂H). The K_a of formic acid is 1.77 × 10^-4. A)3.843 B)3.647 C)13.90 D)10.16 E)4.954

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The correct answer is A because the pH of a 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 1.77 × 10-4, the concentration of the conjugate base (sodium formate) is 0.278 M, and the concentration of the acid (formic acid) is 0.222 M. Plugging these values into the equation, we get: pH = 1.77 × 10-4 + log(0.278/0.222) = 3.843.

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