Precipitation Titration

Precipitation titration is a type of titration in which a precipitate is formed during the titration procedure. The titrant combines with the analyte and generates an insoluble material in precipitation titration, which is repeated until the last drop of the analyte is consumed. The most common method for determining the presence of halogen and metal ions is precipitation titration. Precipitation titration is essential in chemistry because it precisely determines the concentration of halogens and some metal ions in a sample solution.

Example of Precipitation Titration

Here is a detailed example of precipitation titration. 

We can titrate a sample solution with a known concentration of silver nitrate solution to measure the chloride ion concentration.

The chemical reaction that follows is:

Ag+(aq) + Cl–(aq)→ AgCl(s).

• AgCl settles to the bottom of the conical flask as a white precipitate during the titration.
• The amount of silver ion used to achieve the equivalence point is the same as the initial amount of chloride ion. The amount of silver ion used for the equivalence point is the same as the initial amount of chloride ion.

Types of Precipitation Titration

There are three main types of precipitation titration, named after the scientists who discovered them.

Volhard’s Method of Precipitation Titration

Jacob Volhard, a German chemist, developed the method in which silver ions are used to determine anions such as halides, phosphate, and chromate in an acidic media. This method is critical to conduct this titration in an acidic media to avoid the precipitation of iron ions as hydrated oxide. The chloride in the solution is transformed into silver chloride using this reaction technique with an excess of silver nitrate. The potassium thiocyanate solution is used to treat the remaining silver nitrate from the reaction. A complex is created when an excess thiocyanate reacts with an indicator that produces a red colour when reacting with the ferric ammonium sulphate indicator.

Fajan’s Method of Precipitation Titration

American chemist Kazimierz Fagan described a method of precipitation titration where the indicator absorption method is employed in the procedure. Dichlorofluorescein was used as an indicator in this approach, and excess methyl chloride ions were absorbed on the silver chloride surface. The green AgCl suspension turns pink, indicating the endpoint, which is a complex of AgCl and indicator.

Mohr’s Method of Precipitation Titration

German chemist Karl Friedrich Mohr developed the Mohr method of precipitation titration, known as direct titration, using a chloride ion solution as the analyte and silver nitrate as the titrant. Potassium chromate is used as a titration indicator in this method. After chloride ions have been consumed, reddish-brown precipitate forms due to the reaction between silver and chromate ions.

Determination of Endpoint in Precipitation Titrations

Titrations of Ag+ are referred to as argentometric titrations. Three classic approaches based on colour markers can be employed to identify the endpoint in argentometric titration.

• The production of colourful precipitate at the endpoint of a Mohr’s titration.
• The production of a soluble, colourful compound at the endpoint of Volhard’s titration.
• Adsorption of a coloured indicator to the precipitate at the endpoint in Fajan’s titration.

Applications of Precipitation Titration

There are various applications of precipitation titration. The most typical application is for reactions when the titration cannot be recognised by changing the colour. Precipitation titration is commonly used to determine halide ions or silver concentration using sodium chloride (NaCl) solution. It can also determine the ion concentration in an analyte sample. Moreover, it is used to determine how much salt is present in things like water, food, and drinks. It also has pharmaceutical uses, such as carbromal analysis, sodium chloride (NaCl) and potassium chloride (KCl) infusion, among others. Titration by precipitation is also used to determine the salt content of food, beverages, and water.

Things to Remember 

• Titration is an analytical technique for determining the concentration of an unknown liquid.
• The process of precipitation is the transformation of a dissolved substance into an insoluble form.
• A precipitate is a solid that forms during the precipitation process.
• Precipitation titration is a method for determining the concentration of an unknown solution by producing a precipitate from the solution of a known concentration solution.
• The titrant is a solution with a known concentration.
• An analyte refers to a solution with an undetermined concentration.

Conclusion  

Precipitation titration is a type of titration in which precipitation forms at the endpoint of the titration. Precipitation titrations are a type of reaction utilised in a variety of businesses worldwide. They are useful because they enable a highly exact response endpoint identification, otherwise requiring a visual determination using now-antiquated methods.