Question

If you dissolve 0.1 mol of formic acid in 1 L of water, ther esulting solution contains 0.004 mol of H₃O+. Based on this information, is formic acid a strong acid, or is it a weak acid?

Please explain!

Answer 1

We know

Any acid

• Containing carbon is weak
• Containing no carbon is strong

Formic acid stands for HCOOH

It contains C means dissociation is less .

The dissociation of H+ is less means acidity is less.

• Weak acid

Answer 2

In an ideal case, the acid would completely protonate. such an acid would be a strong acid. Dissociation of Formic acid looks like:

HCOOH + H₂O → COOH⁻ + H₃O⁺

one mole of formic acid should give one mole of Hydronium(H₃O⁺) ions

similarly, 0.1 moles of formic acid should produce 0.1 moles of hydronium ions. but we know that it is not the case, a much lesser amount is actually formed.

Which means that Formic acid did not completely dissociate into COOH⁻ and H⁺ ions.

Hence, Formic Acid is a weak acid