Formic acid, which is a component of some insect venoms, has a K_a = 1.8 × 10^-4. What is the [H₃O⁺] in a solution that is initially 0.10 M formic acid, HCOOH? A) 4.2 × 10^-3^M B) 8.4 × 10^-3^M C) 1.8 × 10^-4^M D) 1.8 × 10^-5^M E) 1.8 × 10^-6^M

Question

Quizplus · Accepted Answer

The concentration of H3O+ in a 0.10 M formic acid solution can be found using the formula for the dissociation constant, Ka = [H3O+][HCOO-]/[HCOOH]. Assuming [H3O+] = [HCOO-] and [HCOOH] ≈ 0.10 M (since dissociation is small), we get Ka = [H3O+]^2/0.10. Solving for [H3O+] with Ka = 1.8 × 10^-4 gives [H3O+] = sqrt(1.8 × 10^-4 * 0.10) = 4.2 × 10^-3 M.

Formic Acid, Which Is a Component of Some Insect Venoms