Answer:
Formic acid can react to water, to give protons to medium:
HCOOH + H₂O → H₃O⁺ + HCOO⁻
Weak acid Base Acid Strong conjugate base
HCOO⁻ + H₂O ⇄ HCOOH + OH⁻ Kb
Strong base Acid Weak acid Base
So the formate can take a proton from water to become formic acid again and that's why it is a conjugate strong base.
Explanation:
HCOOH → Formic acid
To determine the conjugate pair and to know if they are weak or strong, we should know, if they can react to water. This is called hydrolisis.
For example: formic acid is a weak acid, so the formed formate will be its conjugate base and it will be strong because the formate can react to water, to make formic again.
Weak acid → Strong conjugate base
Strong acid → Weak conjugate base
Weak base → strong conjugate acid
Strong base → weak conjugate acid
For example HCl is a strong acid. When it is in aqueous solution, we have protons and chlorides.
HCl + H₂O → H₃O⁺ + Cl⁻
Chloride will be the weak conjugate base, because it can't react to water.
We can not make HCl again, according to this equation:
Cl⁻ + H₂O ← HCl + OH⁻ This is impossible.
Formic acid can react to water, to give protons to medium:
HCOOH + H₂O → H₃O⁺ + HCOO⁻
Weak acid Base Acid Strong conjugate base
So the formate can take a proton from water to become formic acid again and that's why it is a conjugate strong base.
HCOO⁻ + H₂O ⇄ HCOOH + OH⁻ Kb
Strong base Acid Weak acid Base
