Farmers who raise cotton once used arsenic acid, H₃AsO₄, as a defoliant at harvest time. Arsenic acid is a polyprotic acid with K₁= 2.5 × 10^-4, K₂= 5.6 × 10^-8, and K₃= 3 × 10^-13. What is the pH of a 0.500 M solution of arsenic acid?

Question

Quizplus · Accepted Answer

The pH is primarily determined by the first dissociation constant (K1) because it is much larger than K2 and K3. Using the approximation for a weak acid, pH = -log(sqrt(K1 * C)), where C is the concentration. This gives pH ≈ 1.96.

Farmers Who Raise Cotton Once Used Arsenic Acid, H3AsO4, as a Defoliant

Farmers Who Raise Cotton Once Used Arsenic Acid, H₃AsO₄, as a Defoliant