titration of phosphoric acid in presence of excess h2po4-,
changes in equivalence point??
In a titration of phosphoric acid (H₃PO₄) in the presence of excess H₂PO₄⁻, the equivalence point is the point at which the amount of reactant being titrated exactly matches the amount of the titrant being added. At this point, the reaction is complete, and the solution reaches a neutral pH.
During the titration, the pH of the solution changes as the titrant is added. However, in the presence of excess H₂PO₄⁻, the pH at the equivalence point is slightly different than what you would expect.
Phosphoric acid (H₃PO₄) is a weak acid with three ionizable protons. In the presence of excess H₂PO₄⁻, the pH at the equivalence point is slightly acidic rather than neutral. This is because the excess H₂PO₄⁻ acts as a buffer, maintaining an acidic pH.
To determine the exact changes in pH at the equivalence point, you can perform a calculated analysis using the concentrations and dissociation constants of H₃PO₄ and H₂PO₄⁻, along with the titrant being used. This involves setting up and solving equilibrium equations to find the concentrations of all species present at the equivalence point.
Alternatively, you can conduct actual titration experiments in the laboratory to determine the pH at the equivalence point. By adding the titrant (e.g., sodium hydroxide) slowly and measuring the pH of the solution after each addition, you can observe the pH changes until you reach the equivalence point. A pH indicator can be used to determine when the solution becomes slightly acidic.
It is important to note that the exact pH changes at the equivalence point will depend on the specific concentrations and dissociation constants of the acids and bases involved, as well as other factors such as temperature and ionic strength.