Learn about the advantages as well as disadvantages of precipitation titration, Mohr method, Fajan method, and Vollhard method.
Chemical analysis plays an important role in chemistry; they are broadly divided into two types of qualitative and quantitative analysis. Titration, also known as titrimetry, is an analytical technique that is commonly used to determine the concentration of an analyte in a sample solution. Acid-base, redox (oxidation-reduction), and precipitation titration are the types of titration. In each type involves a different type of chemical reaction and principle. They are used in a wide variety of applications in industries and research.
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Titration is performed using a burette which is filled by a known concentration of titrant over a conical flask or beaker containing a solute. The titrant is added dropwise until the reaction is completed, and the endpoint or equivalence point is indicated by the indicator used in the reaction.
What is precipitation titration?
Precipitation titration is a type of titration in which a precipitate is formed during the titration reaction. The titrant reacts with the compound to form an insoluble material (precipitate). It employs silver ions to determine chloride levels and continues until all of the compounds have been consumed. Precipitation titration refers to the volumetric process which is based on the formation of a slightly soluble precipitate; however, the argentometric technique refers to precipitating titration using silver nitrate (AgNO3) as a precipitating agent. Precipitation titration has three types, Mohr method, Vollhard method, and Fajan method.
Advantages of precipitation titration:
- The major advantage of precipitation titration is that it is a common method for measuring the presence of halide ions and certain metal ions in a solution, as well as the salt content of food, drinks, and water.
- The major advantage of the Mohr method is that it is a simple, direct, and precise method for chloride determination.
- The major advantage of the Fajan method is that it can selectively work with different indicators over different pH ranges.
- The major advantage of the Volhard method is that it has the ability to performing direct silver and indirect halide analysis, and the endpoint provides very clear color changes.
- It can provide the rapid and precise result of the analysis.
- Minimum and generally used laboratory apparatus such as burette, pipette, funnel, conical flask, beaker, burette stand, wash bottle are required.
- It is feasible to automate the process.
- There is no need of highly specialized chemical knowledge.
Disadvantages of precipitation titration:
- The major disadvantage of precipitation titration over other titration methods is that it requires more skill and practice to achieve effective results.
- The major disadvantage of Mohr titration is that it works only at a pH between 7 and 10 (alkaline solution only) since the chromate ion is the conjugate base of the week chromic acid.
- Another limitation of the Mohr method is it is not suitable for iodide, and in the reaction, it requires a blank.
- The major disadvantage of the Fajan method is that it has difficulty in dilute solution; it should not have high background ionic level.
- The major advantage of the Volhard method is that it has some problems with specific anions.
- Equipment used in titration must be calibrated appropriately as this will affect the final result.
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