Fajans method in Precipitation titrations
Fajans method is a technique used in precipitation titrations to determine the concentration of anions in a solution. It is also known as the adsorption indicator method or the adsorption analysis.
In this method, a known amount of silver nitrate (AgNO3) solution is added to the sample containing the anions. The silver ions combine with the anions in the solution to form a precipitate of insoluble silver salt.
A small amount of adsorption indicator, such as dichlorofluorescein or xylenol orange, is added to the solution. The adsorption indicator is an organic molecule that can adsorb onto the surface of the precipitate, and its color changes as the concentration of free silver ions in the solution decreases.
The titration is carried out by slowly adding the silver nitrate solution to the sample, while continuously stirring the solution. The point at which the color of the adsorption indicator changes is noted as the endpoint of the titration.
The concentration of the anions in the solution can be calculated by determining the amount of silver nitrate solution added to reach the endpoint, using stoichiometry of the reaction.
The Fajans method is particularly useful for the estimation of anions that form insoluble salts with silver ions, such as chloride, bromide, and iodide. The method can be used in a wide range of samples, including water, pharmaceuticals, and industrial products.
One of the major advantages of the Fajans method is that it is relatively simple and requires only a small amount of sample and reagents. However, the method is susceptible to interference from other ions in the solution, and the endpoint can be difficult to detect accurately.
Overall, the Fajans method is a useful technique in precipitation titrations, particularly for the estimation of anions in a wide range of samples.
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