Question

Explain why when a strong acid is titrated with a strong base, the pH at equivalence pt. is equal 7, while in the case of a weak acid (e.g., HC2H3O2) titrated with a strong base (NaOH) pH at equivalence point is above 7

Answer 1

Step-by-step explanation:

The pH of a strong acid when titrated with a strong base is equal to 7 because of the formation of a neutral salt which corresponds to pH = 7.

But on the other hand,

The titration of the weak acid and strong base, the reaction taking place is:

HC₂H₃O₂ + OH⁻ ⇒ H₂O + C₂H₃O₂⁻

At the equivalence point, the pH is greater than 7 because of the conjugate base formed in the above reaction which gives OH⁻ in the solution as:

C₂H₃O₂⁻ + H₂O ⇒ HC₂H₃O₂ + OH⁻

The hydroxide ions produced in the above reaction results in the pH above 7 (basic).