Precipitation Titration

It is a titrimetric method in which the formation of precipitates occurs during the course of the titration experimentation. Titrant reacts with the analyte, resulting in the formation of an insoluble substance. The titration procedure is repeated until the last drop of the analyte has been consumed. When the titrant concentration is too high, it reacts with the indicator and signals that the titration process should be stopped.

Precipitation titration example:

We’ve gone over an example of precipitation titration here in this section.

Consider the following example: To find out the concentration of chloride ion in a specific solution, we can titrate the solution with silver nitrate solution (whose concentration is known). The following is the chemical reaction that takes place:

             Ag+(aq) + Cl-(aq) – AgCl(s)

During the titration, a white precipitate of AgCl can be seen settling at the bottom of the flask, indicating that it has formed. The amount of silver ion used to reach the equivalence point is the same as the amount of chloride ion that was originally present in the solution.

We can use the formula n = cV to calculate the number of moles of chloride ion or silver ion in a solution.

(Molarity is defined as the concentration of a substance in a solution of one part per million of water.)

For the purpose of calculating the volume of the added solution or the molar concentration of ions, it is necessary to know the corresponding values of either of the ions.

Types of precipitation titration:

Volhard’s Method:

The titration of bromides, iodides, and chlorides in an acidic medium is the objective of this methodology. When the chloride in the solution reacts with an excess of silver nitrate solution, the chloride is converted to silver chloride. The amount of leftover silver nitrate is calculated by comparing it to a solution of potassium thiocyanate. When all of the thiocyanate has consumed all of the silver, the excess thiocyanate is made to react with an indicator to indicate that the process is complete. When it reacts with the ferric ammonium sulfate indicator, it produces a red color, and a ferrous thiocyanate complex is formed as a result.

Fajan’s Method:

This method makes use of the reaction that occurs between the precipitate that has formed and the indicator. Dichlorofluorescein is the indicator that is used because it behaves as an anion in solution. Because of an excess of chloride ions in chloride solution, they precipitate and form the primary layer of the precipitate. The sodium cations contribute to the formation of the second layer. The reaction is terminated with an excess of silver ions. Thus, the positively charged silver ion serves as the primary layer, attracting indicators to form a second layer on top of the primary layer. The color of the indicator indicates that the reaction has come to an end.

Mohr Method:

To determine the concentration of chlorides in neutral solution, this method is used. In acidic conditions, the chromate ion is protonated, resulting in the formation of chromic acid. As a result, there is no precipitate formed on the surface. Silver hydroxide is formed as a result of the formation of highly alkaline solutions. This formation results in a brown color, which indicates that the formation has reached its conclusion.

Application of precipitation titration:

Precipitation Titration Has a Wide Range of Applications, 

• It is employed in the determination of the presence of halide ions in a solution.
• It is used to determine the amount of salt present in foods, beverages, and water.
• It is employed in the production of sulfur, thiocyanate, dichromate, and other compounds.
• Precipitation titration can be used to analyze a wide range of drugs, including carbromal, KCl infusion, NaCl infusion, and others.
• It can be used to determine the concentration of anions in an analyte by measuring the pH of the solution.

Conclusion:

Precipitation titration is a type of titration in which the formation of precipitate occurs as a result of the titration procedure itself.

It is a titrimetric method in which the formation of precipitates occurs during the course of the titration experimentation. Titrant reacts with the analyte, resulting in the formation of an insoluble substance. There are three types of precipitation titration i.e, volhard’s method, mohr method and fajan’s method. 

Precipitation titration is used to determine the amount of salt present in foods, beverages, and water. It is employed in the production of sulfur, thiocyanate, dichromate, and other compounds. It can be used to determine the concentration of anions in an analyte by measuring the pH of the solution.