Precipitation Titration - Definition, Types & Example

Precipitation Titration


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Titration is a technique used in analytical chemistry to determine concentration of unknown solution by using solution of known concentration. Solution of known concentration is known as titrant while solution of unknown concentration is known as analyte in titration technique. Precipitation titration is a type of titration which involves formation of precipitate during titration at end point. In this article we will discuss mainly precipitation titration definition with example and argentometric titration (a type of precipitation titration), Volhard method, Fajan’s method, Mohr’s method and difference between Mohr’s method and Volhard’s method. 

What is Precipitation Titration?

Precipitation titration is a type of titration which involves the formation of precipitate during the titration technique. In precipitation titration, the titrant reacts with analyte and forms an insoluble substance called precipitate. It continues till the last amount of analyte is consumed. It is used to determine chloride by using silver ions. 

Principle of Precipitation Titration 

The principle of precipitation titration can be shown as follows – 

Quantity of added precipitating reagent = quantity of substance being precipitated 

Precipitation Titration Curve 

In precipitation titration curve, a graph is drawn between change in titrant’s concentration as a function of the titrant’s volume. A precipitation titration curve is given below for 0.05M NaCl with 0.1M AgNO3


Reaction involve is as follows – 

AgNO3 + NaCl 🡪 AgCl + NaNO3

Precipitation titration example 

Determination of concentration of chloride ions in a solution by using silver ions of a known solution is an example of precipitation titration. Reactions involved are as follows – 

AgNO3      +         Cl-                                                               🡪                                 AgCl       +          NO3

              (in solution of NaCl)                                                        (White ppt)

Argentometric Titration 

It is a type of precipitation titration which involves the use of silver ion. Symbol of silver is Ag which is taken from its latin name argentum. So, word argentometric is also taken from latin word argentum. 

Methods of Argentometric Titration

  • Volhard’s Method 

  • Fajan’s Method 

  • Mohr’s Method 

Volhard’s Method 

German Chemist- Jacob Volhard

This method was first given by German Chemist, Jacob Volhard in 1874. This method involves the determination of halide (F, Cl, Br, I) ions, anions like phosphate, chromate in acidic medium by using silver ions. This titration must be performed in acidic medium otherwise iron ion get precipitated as hydrated oxide. Iron ion is used as indicator in Volhard’s method. In this method 1st analyte (halide ion solution or any other anionic solution) is titrated with measured excess of AgNO3

Reaction – If analyte contains chloride anions. The reaction will be as follows - 

Cl- + Ag+ 🡪 AgCl + Ag+ (in excess)

Now the unreacted or in excess silver ions are titrated with standard solution of KSCN using iron ion (Fe+3) as indicator which gives red color in the end point. 

Reaction – The reaction can be shown as follows- 

Ag+ + SCN- 🡪 AgSCN 

Now as the thiocyanate ion will be in excess in the titration mixture, red colour appears which is due to formation of FeSCN(II) compound. 

Reaction – Reaction involved can be shown as follows – 

Fe+3 + SCN- 🡪 FeSCN+2

                         (Red colored compound)

It is an indirect method of precipitation. 

Fajan’s Method 

American Chemist – Kazimierz Fajan

This method was given by American chemist Kazimierz Fajan. That’s why it is known as fajan’s method. This method is also known as indicator adsorption method because in this method chloride ions present in excess are adsorbed on silver chloride surface. In this method dichlorofluorescein is used as an indicator. The end point is determined by green suspension (of AgCl and incidation) turning pink (complex of AgCl and indicator). 

Reaction – reaction involved can be written as follows – 

Ag+ + Cl- 🡪 AgCl 

Ag+ + AgCl + Indicator 🡪 AgCl-Ag+ Indicator 

It is a direct method of precipitation. 

Mohr’s Method 

Karl Friedrich Mohr

This method was given by Karl Friedrich Mohr, a German Chemist. That’s why this method is called Mohr’s method. It’s a direct titration method. In this method silver nitrate is used as titrant and chloride ion solution as analyte. Potassium chromate is used as indicator. At the end point, when all chloride ions are consumed by silver ion, reddish brown colored precipitate is formed by reaction of silver ion and chromate ion. 

Reaction- Reaction involved can be written as follows – 

AgNO3      +         Cl-                                                               🡪                                 AgCl       +          NO3

              (in solution of NaCl)                                                        (White ppt)


At the end point – 

2Ag+ + CrO4-2 🡪 Ag2CrO4

                           (Reddish Brown ppt)


Difference Between Mohr’s Method and Volhard’s Method

S.No.

Volhard’s Method 

Mohr’s Method 

1.

It is an indirect method of titration. 

It is a direct method of titration. 

2.

In this method, red precipitate of ferric thiocyanate is formed which indicates end point of the titration. 

Fe+3 + SCN- 🡪 FeSCN+2

(Red colored compound)

In this method, red precipitate of silver chromate is formed which indicates end point.

2Ag+ + CrO4-2 🡪 Ag2CrO4

(Reddish Brown ppt)

3.

Condition for titration should be acidic. Otherwise iron ion forms hydroxide ions.

Condition for titration should be neutral to alkaline. 

4.

By this method, we can determine the concentration of halides. 

By this method, titration of iodide and cyanate is not possible. 

5.

This titration is carried out below 20

This titration can be carried out under room temperature. 

Applications of Precipitation Titration 

  • It is used for the determination of halide ions in the solution. 

  • It is used to measure salt content in food, beverages and water. 

  • It is used for Sulphur, thiocyanate, dichromate etc. 

  • Many drugs such as carbromal, KCl infusion, NaCl infusion etc. can be analysed by precipitation titration. 

  • It can be used for the determination of concentration of anions in the analyte. 

Precipitation titration is an important topic for Class 12. Many practical based questions are asked in the final board exam of CBSE Class 12 Chemistry. If you want to read more on the topic, register yourself on Vedantu and go through the study material, NCERT Solutions for CBSE Class 12 etc. provided by Vedantu as free PDFs. You can also attend online classes provided by highly qualified teachers at Vedantu.