Post a Comment. Home Education T-BP Daily, we undergo several chemical reactions. The reactions that taken place during the cooking and digestion of food are examples of these, Among chemical reactions, precipitation reactions fall into this category. A soluble salt which is in an aqueous solution is combined with another salt which is in an aqueous solution to form two products. A few of these precipitate out of solution because they are insoluble in the solution and are therefore called precipitates.
A precipitation reaction is the formation of insoluble salts from the combination of two ionic bonds in an aqueous solution. Precipitates are salts that are insoluble in water but form during precipitation reactions.
Reactions involving precipitation result in solid residues called precipitates due to the double displacement involved. As well, insoluble salts may form as the result of the precipitation of salts when two or more solutions with different salts are mixed. Mohr method works in the PH range of only. Above this PH, silver will form a precipitate with hydroxide.
Below this PH, chromate converts to dichromate, a bright orange color thereby obscuring the endpoint. Calcium carbonate is often added to reduce the acidity of the solution. This method was first given by German Chemist, Jacob Volhard in This method involves the titration of bromides, iodides and chlorides, in an acidic medium.
The chloride in the solution is converted to silver chloride when reacted with excess silver nitrate solution. The leftover silver nitrate is estimated against potassium thiocyanate solution. However, after all the silver ions are used, the thiocyanate will react with ferric ions. In this experiment, the indicator system is very sensitive, and it usually gives better results.
However, we have to keep the solution acidic because the ferric ions tend to form ferric hydroxide in the presence of the basic medium. Fajans method is an analytical technique in which we can determine the halide concentration through adsorption. In this method, the fluorescein and its derivatives are adsorbed on to the surface of colloidal silver chloride.
After these adsorbed ions occupy all the chloride ions, the addition of another drop of fluorescein reacts with the silver ions, forming a red colour precipitate. Whereas, Fajans method refers to the adsorption reaction between silver halide and fluorescein. Mohr method, Volhard method, and Fajans method are important analytical techniques that can be used as precipitation reactions to determine the halide concentration in a given sample.
Mohr method is the reaction between silver ion and halide ion in the presence of chromate indicator, while Volhard method refers to the reaction between excess silver ions and halide ions. Fajans method, on the other hand, refers to the adsorption reaction between silver halide and fluorescein.
So, this is the key difference between Mohr Volhard and Fajans methods. Rahman, Ashikur. Difference between endpoint and equivalence point. Difference between volumetric analysis and titration. Difference between gravimetric and volumetric analysis. Difference between coulometric and volumetric titration. Difference between iodometric and iodimetric titration. Difference between acid-base titration and redox titration.
Difference between aqueous and non-aqueous titration. Difference between back titration and direct titration. Difference between titrant and titrand. Difference between standardization and titration. Labels: mohr's method , Volhard method. No comments:. Newer Post Older Post Home. Subscribe to: Post Comments Atom.
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