Write a principle of Mohr’s method.
Answers
Answer:
This method determines the chloride ion concentration of a solution by titration with silver nitrate. As the silver nitrate solution is slowly added, a precipitate of silver chloride forms. The end point of the titration occurs when all the chloride ions are precipitated.
Mohr's Method was given by a German scientist, K.F. Mohr.
Mohr's Method is commonly used in titrations for the formation of a precipitate. This is done in order to detect the presence of an ion or a compound. It is a direct titration method. It is used to determine the chloride ion concentration of a given solution. We titrate the solution with silver nitrate (AgNO₃) and use potassium chromate (K₂CrO₄) as an indicator.
Following reactions take place:
On adding the silver nitrate, the precipitate of silver chloride is formed
AgNO₃ + Cl⁻ → AgCl(s) + NO₃⁻
The reaction is said to reach its endpoint when all the chloride ions are precipitated as AgCl. The remaining silver ions react with chromate (CrO₄⁻⁻) to form silver chromate. Silver chromate forms a red-brown precipitate.