For the reaction of deprotonation of formic acid, the concentration of HCOO⁻ at equilibrium is 0.0151 M if the initial concentration of formic acid is 1.35 M.
The reaction of deprotonation of formic acid is the following:
CHOOH + H₂O ⇄ HCOO⁻ + H₃O⁺
At the equilibrium we have:
CHOOH + H₂O ⇄ HCOO⁻ + H₃O⁺ (1)
1.35 - x x x
The acid <em>equilibrium </em>constant for this reaction is:
(2)
Entering the values of [CHOOH] = 1.35-x, [HCOO⁻] = [H₃O⁺] = x, into equation (2) we have:

After solving the above <em>quadratic equation</em> and taking the positive value for x (<u>concentrations cannot be negative</u>), we have:
Therefore, the concentration of HCOO⁻ at equilibrium is 0.0151 M.
Learn more about the equilibrium constant here:
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