Determination of silver indirect method

This particular titration is well adapted to be carried out potentiometrically (Section 15.24). 

Procedure (a). Prepare the indicator by grinding 0.1 g murexide with 10 g of potassium nitrate use about 50 mg of the mixture for each titration. 

Also prepare a 1M solution of ammonium chloride by dissolving 26.75 g of the analytical grade solid in de-ionised water and making up to 500 mL in a graduated flask. 

Pipette 25 mL nickel solution (0.01 M) into a conical flask and dilute to 100mL with de-ionised water. Add the solid indicator mixture (50mg) and 10 mL of the 1M ammonium chloride solution, and then add concentrated ammonia solution dropwise until the pH is about 7 as shown by the yellow colour of the solution. Titrate with standard (0.01 M) EDTA solution until the end point is approached, then render the solution strongly alkaline by the addition of 10 mL of concentrated ammonia solution, and continue the titration until the colour changes from yellow to violet. The pH of the final solution must be 10 at lower pH values an orange-yellow colour develops and more ammonia solution must be added until the colour is clear yellow. Nickel complexes rather slowly with EDTA, and consequently the EDTA solution must be added dropwise near the end point. 

Procedure (b). Prepare the indicator by dissolving 0.05 g bromopyrogallol red in 100 mL of 50 per cent ethanol, and a buffer solution by mixing 100 mL of 1M ammonium chloride solution with 100 mL of 1M aqueous ammonia solution. 

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