Understanding Equivalence Point
The equivalence point in a titration is the point where the moles of acid and base are stoichiometrically equal. At this point, the reaction is complete, and the solution contains only the salt formed by the neutralization reaction.
Salt Hydrolysis
The pH at the equivalence point depends on whether the salt formed is:
* Neutral: The salt does not hydrolyze (react with water) to produce H+ or OH- ions. The pH will be 7. This occurs when a strong acid is titrated with a strong base, or vice versa.
* Acidic: The salt hydrolyzes to produce H+ ions, making the solution acidic. This occurs when a strong acid is titrated with a weak base.
* Basic: The salt hydrolyzes to produce OH- ions, making the solution basic. This occurs when a weak acid is titrated with a strong base.
Examples:
* Strong acid-strong base: HCl (strong acid) + NaOH (strong base) → NaCl (neutral salt) pH = 7
* Strong acid-weak base: HCl (strong acid) + NH3 (weak base) → NH4Cl (acidic salt) pH < 7
* Weak acid-strong base: CH3COOH (weak acid) + NaOH (strong base) → CH3COONa (basic salt) pH > 7
In summary:
The pH at the equivalence point is determined by the relative strengths of the acid and base involved in the titration. The salt formed dictates whether the solution is acidic, basic, or neutral, ultimately affecting the pH.
