I am having trouble with this problem... Help please!
1. Formic acid (HCO2H) has a dissociation constant of 1.8 × 10-4 M. The acid dissociates 1:1. What is the [H+] if 0.35 mole of formic acid is dissolved in 1.0 liter of water? Use a scientific calculator.
(Points : 3)
0.9 × 10 ^-3 M

7.9 × 10^ -3 M

15 × 10^- 4 M

21 × 10^- 4 M

Question

I am having trouble with this problem... Help please! 
1. Formic acid (HCO2H) has a dissociation constant of 1.8 × 10-4 M. The acid dissociates 1:1. What is the [H+] if 0.35 mole of formic acid is dissolved in 1.0 liter of water? Use a scientific calculator.
(Points : 3)
        0.9 × 10 ^-3 M

        7.9 × 10^ -3 M

        15 × 10^- 4 M

        21 × 10^- 4 M

aaronq · Answer

use an ICE table and the eq. expression.

$K=\dfrac{[H^+][CO_2H^-]}{[HCO_2H]}$