Question:
In argentometric titration, fluorescein is used as an indicator. This is due to
In argentometric titration, fluorescein is used as an indicator. This is due to
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Fajans method uses \textbf{adsorption indicators}.
The colour change occurs due to adsorption of the indicator on the surface of the precipitate at the equivalence point.
Updated On: Jul 9, 2026
- Adsorption of fluorescein on the surface of AgCl
- Absorption of fluorescein by AgCl
- Complex formation of fluorescein with \(\mathrm{Ag^+}\)
- Oxidation of AgCl to \(\mathrm{AgClO_3}\) \bigskip
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The Correct Option is A
Solution and Explanation
Step 1: Principle of Fajans method.
Argentometric titration using fluorescein is based on the adsorption indicator principle.
Step 2: Role of fluorescein. Near the end point, the AgCl precipitate acquires a positive surface charge due to excess \(\mathrm{Ag^+}\) ions. The negatively charged fluorescein ions are adsorbed on the surface of AgCl, producing a distinct colour change.
Step 3: Final conclusion. Thus, fluorescein acts because of its \[ \boxed{\text{adsorption on the surface of AgCl}.} \] Hence, the correct option is \(\boxed{(A)}\).
Step 2: Role of fluorescein. Near the end point, the AgCl precipitate acquires a positive surface charge due to excess \(\mathrm{Ag^+}\) ions. The negatively charged fluorescein ions are adsorbed on the surface of AgCl, producing a distinct colour change.
Step 3: Final conclusion. Thus, fluorescein acts because of its \[ \boxed{\text{adsorption on the surface of AgCl}.} \] Hence, the correct option is \(\boxed{(A)}\).
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