Question

Why does the surface charge of a precipitate change sign atthe equivalence point?

Short answer

There is a shift in sign beyond the equivalence point due to extra silver ions on the precipitate.

Step-by-step solution

 Step 1: Define equivalence point and fajan’s method

The chemical equivalency point of a reaction is the point at which equivalent amounts of reactants are chemically combined. In other words, it is a point during titration when the amount of additional titrant is sufficient to totally neutralise the analyte solution.

The amount of chloride in a particular sample is determined using Fajans method, which involves treating a chloride solution with a predetermined concentration of silver nitrate. Silver chloride precipitate is formed when silver ions and chloride ions react together.

Explain Why does the surface charge of a precipitate change sign atthe equivalence point.

To explain: The reason for the change in sign of the surface charge of the precipitate is that there are more chloride ions present when silver ion titrates against chloride ions before reaching the equivalence point.

Excess chloride ions are adsorbed on the silver chloride surface, resulting in an increase in negative charge.

Beyond the equivalency point, more silver ions are present in solution, giving the precipitate a larger positive charge.

There is a shift in sign beyond the equivalence point due to extra silver ions on the precipitate.