Acid Base Chemistry (Answer Completely)

Question

Formic acid, whose formula is HCOOH, is the active ingredient in ant bite stings. A 0.10 M aqueous solution of formic acid has a pH of 2.38. What is K_a for formic acid?

Answer 1

HCOOH ==> H⁺ + HCOO^-

Ka = [H⁺][HCOO^-]/[HCOOH

From the pH = 2.38, we can find [H⁺]

[H⁺] = 1x10^-2.38 = 4.17x10^-3 M. This is also [HCOO^-]

Ka = (4.17x10^-3)(4.17x10^-3) / 0.10

Ka = 1.74x10-4