AS silver ions first react with Cloride ions in the sample(equivalence point) and when all the chloride ions are consumed we have to add more silver nitrate solution to increase its concentration to a level where it can precipitate chromate ions as silver chromate precipites (reddish brown ppts) this is the end point . so remove this error of equivalence point detection we take the same volume of indicator (chromate solution) in a flask labelled blank and add water into this flask (the same volume as that of sample solution) and then titrate this blank labelled flask with standard silver nitrate solution and note the volume of titrant consumed (blank volume),then calculations for real equivalence point can be made as:
equivalence point=(end point)-(blank volume)
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Blank titration is necessary in the Mohr method to account for any impurities present in the reagents or in the sample. It helps to ensure that the color change observed during the titration is solely due to the analyte of interest being titrated, and not influenced by impurities that could interfere with the accuracy of the results.
Iodide cannot be determined by Mohr titration because it does not form a precipitate with silver nitrate. Mohr titration relies on the formation of a colored precipitate to indicate the end point, which is not observed in the case of iodide ions. Other methods, such as iodometric titration or spectrophotometry, are used to determine iodide ions quantitatively.
In Mohr's method of titration, the pH is maintained as neutral in order to ensure that the indicator used in the titration changes color sharply at the equivalence point. This helps in accurately determining the end point of the titration, as the color change will be clearly visible when the reaction is complete. Maintaining a neutral pH also prevents any interference from acidic or basic impurities that could affect the accuracy of the titration.
Ferroin indicator is used in the redox titration of Mohr's salt as it changes color when the Fe2+ ions are completely oxidized to Fe3+ ions. This color change helps in determining the end point of the titration, where all the Mohr's salt has been oxidized and no more Fe2+ ions are present.
Hydrochloric acid (HCl) is used in the titration of Mohr's salt and potassium dichromate because it reacts with Mohr's salt to form ferric chloride and with potassium dichromate to form chromium chloride. These reactions result in the formation of a color change in the solution which allows for the end point of the titration to be easily detected.
Mohr salt is named after the German chemist Karl Friedrich Mohr, who first synthesized it in 1855. He discovered the compound's chemical composition and properties that are frequently used in analytical chemistry and titration methods.