Calculate the pH of a solution that is 0.210 M in nitrous acid (HNO₂) and 0.290 M in potassium nitrite (KNO₂). The acid dissociation constant of nitrous acid is 4.50 × 10^-⁴. A) 4.562 B) 3.490 C) 13.86 D) 10.51 E) 3.210

Question

Quizplus · Accepted Answer

The dissociation equation for nitrous acid is: HNO₂ ⇌ H+S1U1BONO₂- The acid dissociation constant, Ka, is given as 4.50 × 10^-. The expression for Ka is: Ka = [H+S1U1B][NO2-S1U1B]/[HNO₂] Since the solution contains both nitrous acid and its conjugate base (potassium nitrite), it is a buffer solution. The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([NO2-S1U1B]/[HNO₂]) Substituting the given values: pH = -log(4.50 × 10^-) + log([0.290]/[0.210]) pH = 3.490 Therefore, the correct answer is B.

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