Answer to Question #303891 in General Chemistry for cornnnfrogeuu

Question

a.      Formic acid, which is a component of insect venom, has a Ka = 1.8 x 10^-4. What is the [H3O⁺] in a solution that is initially 0.20 M formic acid, HCOOH?  (4 pts.)

                HCOOH_(aq)  +  H₂O_(l)   ⇌   H₃O⁺_(aq)    +    HCOO^–_(aq)

(acid-base equilibria)

Answer 1

Answer is: concentration of H₃O⁺ ions is 4.2·10⁻³ M.

Chemical reaction: HCOOH(aq) + H₂O(l) ⇄ HCOO⁻(aq) + H₃O⁺(aq).

c(HCOOH) = 0,1 M.

[H₃O⁺] = [HCOO⁻] = x.

[HCOOH] = 0,1 M - x.

Ka = [H₃O⁺] · [HCOO⁻] / [HCOOH].

0,00018 = x² / (0,1 M - x).

Solve quadratic equation: x = [H₃O⁺] = 0,0042 M.