The major difference between the Mohr and Volhard method is that the Mohr method involves the reaction of silver ions with halide ions in the presence of a chromate indicator, whereas the Volhard method involves the reaction of excess silver ions with halide ions.
Titration, often known as titrimetry, is a volumetric analysis used to determine the amount of analyte in a sample solution. This involves a titrant that is filled in the burette, a pipette used to introduce the analyte into the conical flask, where the reaction takes place. The titrant of known concentration is added until the reaction is completed (Chemical equivalence point). The endpoint of the titration is the point at which the reaction completes.
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To detect the endpoint, an indicator is used that changes color at the endpoint. Alternatively, an instrumental method such as a pH meter, potentiometer, or conductivity meter is also used. There are four types of titrations based on the chemical reaction that occurs between the titrant and the solute, such as acid-base titration, redox titration, complexometric titration, and precipitation titration.
What is precipitation titration?
Precipitation titration is a type of titration in which the formation of a precipitate during the titration process is involved. Precipitation titration refers to the volumetric method that depends on the formation of a slightly soluble precipitate, while argentometric titration refers to precipitation titration using silver nitrate (AgNO3) as the precipitating agent.
Quantity of added precipitating reagent = amount of analyte being precipitated is the principle of precipitation titration. The titrant reacts with a compound to form an insoluble substance called a precipitate. This continues until all compounds have been consumed with silver ions being used to determine chloride levels.
The Mohr, Volhard, and Fajans method are types of precipitation titration are important analytical techniques used to determine the concentration of halide and certain metal ions. These methods are named after the scientists who developed this method.
What is Mohr’s method?
The Mohr method is a type of precipitation titration first described by a German chemist, Karl Friedrich Mohr. It is a direct titration method used to determine the chlorides by titration with silver nitrate.
It uses the chromate ions (CrO42-) as an indicator for the argentometric determination of bromide, cyanide, and chloride ions.
The Mohr method is more effective in the PH range of 06.00 to 09.00, above this pH range, the silver will precipitate with hydroxide. When all of the chloride ions have been consumed by the silver ion, a reddish-brown colored precipitate is formed as a result of the reaction between the silver ion and the chromate ion.
What is the Volhard's method?
The Volhard method is a type of precipitation titration and an example of back titration, first described by a German chemist, Jacob Volhard in 1874. It is used to determine the halide concentration using a back titration, which involves titrating chloride solution with silver ions and then determining the excess silver ion content in the sample.
The indicator in this experiment is a solution containing ferric ions, which can produce a red color with thiocyanate ions. A thiocyanate ion solution is used to titrate the excess amount of silver ions. In this case, the thiocyanate reacts with silver ions rather than ferric ions. The thiocyanate, on the other hand, will react with ferric ions after all of the silver ions have been used. Because ferric ions form ferric hydroxide in the presence of a basic medium, it needs to keep the solution acidic.
Difference between Mohr method and Volhard method:
- In Mohr's titration, silver nitrate is used as the titrant and chloride ion solution as the analyte, while in the Volhard method, excess silver nitrate is used to precipitate chlorides, which is then titrated with potassium or sodium thiocyanate.
- Mohr method is a direct method of titration, whereas the Volhard method is an indirect method of titration.
- In Mohr's titration, at the endpoint, a colored precipitate is formed, whereas in Volhard's titration, at the endpoint a soluble, colored complex is formed.
- Potassium chromate is used as an indicator in the Mohr technique, while ferric ammonium sulfate is used as an indicator in the Volhard method.
- The Mohr method requires neutral or alkaline conditions, while the Volhard method requires acidic conditions.
- The Mohr titration is performed at room temperature, while the Volhard titration is performed at temperatures below 20 degrees Celsius.
- Iodine and cyanate cannot be titrated with the Mohr method, while iodide, bromide, and chloride can be determined with the Volhard method.
Mohr vs Volhard method
Commonly asked questions on titration are as follows.
What is the Fajan method?
Fajan's method is a type of precipitation titration in which silver ions are titrated with halide or thiocyanate ions in the presence of an adsorption indicator. Dichlorofluorescein is a solution-based indicator used in the Fajan method that is an anion in the solution.
What is the basic difference between the Volhard method and the modified Volhard method?
The major difference between Volhard and the modified Volhard method is that the Volhard method is used to determine the chlorine, bromine, and iodine in the form of halides, whereas the modified Volhard method is used to determine the anions that precipitate with silver.
What is the advantage of the Mohr method?
The Mohr method has the advantage of being a simple, precise, and direct method for determining chloride concentration.
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