Introduction
(Image will be uploaded soon)
Titration is a technique used in analytical chemistry to determine the concentration of an unknown solution by using a solution of known concentration. Solution of known concentration is known as titrant while the solution of unknown concentration is known as analyte in titration technique. Precipitation titration is a type of titration which involves the formation of precipitate during titration at the endpoint. In this article, we will discuss mainly precipitation titration definition with example and argentometric titration (a type of precipitation titration), Volhard method, Fagan's method, Mohr’s method, and the 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 the analyte and forms an insoluble substance called a 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 involves 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 a solution of NaCl) (White ppt)
Argentometric Titration
It is a type of precipitation titration which involves the use of silver ions. The symbol of silver is Ag which is taken from its Latin name Argentum. So, the word argentometric is also taken from the 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 an acidic medium otherwise iron ion get precipitated as hydrated oxide. Iron ions are used as indicators in Volhard’s method. In this method, 1st analyte (halide ion solution or any other anionic solution) is titrated with a measured excess of AgNO3.
Reaction – If the 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 a standard solution of KSCN using iron ion (Fe+3) as an 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 the formation of the 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 the 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 indication) 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 an indicator. At the end point, when all chloride ions are consumed by silver ions, reddish brown colored precipitate is formed by reaction of silver ions and chromate ions.
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
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.
Significance of Learning the Concept of Precipitation Titration
Learning the concept of precipitation titration is important for all chemistry students. In this topic, you will learn the various methods of formation of a precipitate using the titration technique. This process is carried out for a number of reasons, such as determining the number of halide ions in a solution, measuring the amount of salt in food items, etc. So, by learning this concept you can improve your understanding of different kinds of reactions involved in the process of precipitation titration. Below are some more reasons why learning the concept of precipitation titration is important for you.
If you have clearly understood the concept of precipitation titration, you will be able to score really well in your exams.
Questions based on precipitation titration are often asked in tests and exams. So, by learning this concept, you will be able to answer these questions and secure a good score.
By learning the process of precipitation titration, you can understand how the precipitate is formed and the different methods used in its formation.
With this topic, you can also learn how precipitation titration is applied and used in multiple areas for different purposes.
The precipitation titration process can be performed through three different methods. By learning this concept, you can differentiate between these methods and analyse which one is more suitable for the process.
Tips to learn the Concept of Precipitation Titration
Learning the concept of precipitation titration will not be that difficult, especially when you are learning with Vedantu. Vedantu provides you with a user-friendly platform comprising a large variety of study resources to help you learn and enhance your knowledge. You can use our study materials for absolutely free. These study materials are curated by some of the best subject experts to ensure high quality and accuracy. Other than the concept of precipitation titration, you can learn different concepts of chemistry with ease.
Besides Vedantu, below are some more tips to help you learn the concept of precipitation titrations.
First, start with your textbook and read the definitions and explanations of precipitation titration provided in the book. This will give you an idea of what this process is about and how it is performed.
After you are done with the textbook, you should use different reference books to gain more knowledge of precipitation titration. These books contain illustrations and examples to help you understand the concept more clearly.
You can try answering the exercise questions given in textbooks and reference books to practice and improve your understanding of the precipitation titration process.
Once you have completely understood the process of precipitation titration, you can explore different sample papers and previous year's chemistry question papers and pick out more questions based on this topic. It will also give you an idea of the difficulty level of questions related to precipitation titration.
Make revision notes by writing down all the important information and creating a summary of the concept of precipitation titration. These notes and summary will help you in quick revisions and make you more efficient.
