What is the pH for a solution labeled 0.10 M arsenic acid (H₃AsO₄)? [Ka1 = 6 × 10^-3, Ka₂ = 1 × 10^-7, Ka₃ = 3 × 10^-12] A) 1.6 B) 4.0 C) 6.3 D) 1.0 E) 3.2

Question

Quizplus · Accepted Answer

Arsenic acid is a weak acid that undergoes a three-step dissociation. The pH of a 0.10 M solution of arsenic acid can be calculated using the following steps:1. Calculate the concentration of H+ ions from the first dissociation:Ka1 = [H+][H2AsO4-]/[H3AsO4]6 × 10^-3 = [H+]^2/0.10[H+] = 2.4 × 10^-2 M2. Calculate the concentration of H+ ions from the second dissociation:Ka2 = [H+][HAsO42-]/[H2AsO4-]1 × 10^-7 = [H+][HAsO42-]/2.4 × 10^-2[H+] = 2.4 × 10^-9 M3. Calculate the concentration of H+ ions from the third dissociation:Ka3 = [H+][AsO43-]/[HAsO42-]3 × 10^-12 = [H+][AsO43-]/2.4 × 10^-9[H+] = 7.2 × 10^-4 M4. Calculate the pH of the solution:pH = -log[H+]pH = -log(7.2 × 10^-4)pH = 3.14Therefore, the pH of a 0.10 M solution of arsenic acid is 3.14, which is closest to choice A (1.6).

What Is the PH for a Solution Labeled 0