Precipitation Titration: Definition, Methods, Applications & Limitations

Precipitation titration is a titration process that helps in formation of precipitate during titration technique. There are three methods of Precipitation Titration: Volhard's Method, Fajan's Method, and Mohr's Method. In precipitation titration, titrant reacts with the analyte and forms an insoluble substance. This process continues till the consumption of the last drop of the analyte. Precipitation Titration is used to determine the presence of halogen and metal ions.

Key Terms: Precipitation Titration, Titrant, Analyte, Silver Chloride precipitate, Volhard Method, Fajan’s Method, Mohr’s Method.

---

What is Precipitation Titration?

[Click Here for Sample Questions]

Precipitation titration is based on the formation of precipitate by the reaction of the sample with precipitating agents. Precipitate formed is the less soluble compound. Titration is a process of determining the concentration of an unknown solution with the help of the solution of the known concentration.

In the process of titration, the solution of known concentration is known as the titrant, and the solution of unknown concentration is known as the analyte. The process of titration is used to check the purity of synthesized compounds mainly in pharmaceuticals.

Through precipitation titration, the precipitates are formed during the process of titration.

Precipitation Titration​

To determine the concentration of chloride ions in a certain solution, the solution can be titrated with a silver nitrate solution of known concentration. The white-coloured precipitate of silver chloride is formed. The quantity of silver ions used to determine the endpoint is equal to the quantity of originally present chloride ions.

Reactions involved in the precipitation titration process are given below:

AgNO₃ + Cl^- →   AgCI + NO₃^-

Precipitation Titration Principle: In the precipitation titration the quantity of participating reagent added is equal to the precipitate.

Quantity of reagent added = Quantity of precipitate obtained

Read More: CBSE Class 12 Chemistry Practical

---

What are the Methods of Precipitation Titration?

[Click Here for Previous Year Questions]

There are mainly three types of precipitation titrations:

1. Volhard’s Method
2. Fajan’s Method
3. Mohr’s Method

All these methods are named based on the scientists who discovered them.

Volhard’s Method

Volhard’s method anions like halides, phosphate, and chromate are determined in an acidic medium by using silver ions. To prevent the precipitation of iron ions as hydrated oxide it is important to perform this titration in an acidic medium.

In this method of reaction with the excess of silver nitrate, the chloride present in the solution is converted into silver chloride. The leftover silver nitrate from the reaction is again treated with potassium thiocyanate solution. The excess of thiocyanate is made to react with an indicator which gives a red color on reacting with the ferric ammonium sulfate indicator and a complex is formed.

Fajan’s Method

Fajan’s method of precipitation titration was given by American chemist Kazimierz Fagan. In this method, the indicator absorption method is used. In this method, dichlorofluorescein worked as an indicator and methyl chloride ions that are present in excess are absorbed on the silver chloride surface.

The endpoint is determined by the green suspension of AgCl which turns pink which is a complex of AgCl and indicator.

Mohr’s Method

Mohr’s method of precipitation titration was given by German Chemist Karl Friedrich Mohr. This is a direct titration method in which silver nitrate is used as titrant and a solution of chloride ion is used as analyte. The indicator used in the titration is Potassium chromate. The reddish-brown precipitate is formed at the end of the reaction of silver ions and chromate ions, after the consumption of all the chloride ions.

---

Application of Precipitation Titration

[Click Here for Sample Questions]

The different applications of precipitation titration are as follows:

1. Precipitation titration is used to determine the halide ions.
2. Precipitation titration is used to measure salt content in various food & beverages.
3. Precipitation Titration is used to analyze various drugs.
4. Precipitation titration is used for analyzing the concentration of the anion in the analyte.

Read More:

---

Limitations of Precipitation Titration

[Click Here for Previous Year Questions]

There are several limitations also in the process of precipitation titration:

• Only very few halide ions can be titrated by using the precipitation titration method.
• Coprecipitation also occurs.
• The endpoint is very difficult to analyze

Read More: Brown Ring Test

---

Previous Year Question

1. What is the mass of the precipitate formed when 50 mL of 16.9% solution … (NEET 2015)
2. In presence of HCl, H₂S results the precipitation of Group-2 elements … (KCET 2015)
3. The mass of AgCl precipitated when a solution containing 11.70 g of NaCl … (KCET 2019)

---

Things to Remember

• Titration is a method of analysis by which the concentration of unidentified liquid is determined.
• Precipitation is the process of transforming a dissolved substance into an insoluble form.
• The solid formed during the process of precipitation is called a precipitate.
• The method in which the concentration of the unknown solution is determined by using the solution of the known concentration solution by forming a precipitate is called precipitation titration.
• The solution of known concentration is called titrant.
• The solution of unknown concentration is called analyte.

Precipitation Titration PDF

Check out: Paper Chromatography