Why add 05 mL of indicator for the Mohr method and only 23 d

Why add 0.5 mL of indicator for the Mohr method, and only 2-3 drops for acid base reactions?

Solution

Answer:

1) Mohr Method : It\'s a Precipitation titration and we expect 100 % precipttion of concerned metal ion . Indicator used is K₂CrO₄ Potassium Chromate. Here after the precipitation of all Cl^- ions as AgCl the excess Ag⁺ ions start getting precipiated by CrO₄^2- ions. To ensure the complete precipitation the excess concentration of CrO₄^2- ions needed to be supplied in the reaction.

Moreover For precipitation of Ag+ as A2CrO₄ requires a neutral medium. Maintannace of neutrality is somewhat difficult as AgOH formed makes pH high and H2CrO₄ formed makes pH low and these things also affect concentration of CrO₄^2- ions and hence for extre surity we use calculated excess of an Indicator.

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2) Acid Base reaction : It\'s purpose is just a qualitative (Quantitative till end point not after end point) i.e. just we need to know end point of the titration and hence a small concenttration of CrO₄^2- ions suffice the work hence 2 / 3 drops are sufficien in acid Base titration.

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