Determination of copper direct titration

The indicator used is fast sulphon black F which is virtually specific in its colour reaction with copper in ammoniacal solution it forms coloured (red) complexes with only copper and nickel, but the indicator action with nickel is poor. 

Procedure. Prepare an indicator solution by dissolving 0.5 g of fast sulphon black F in 100 mL of de-ionised water. 

Pipette 25 mL of the copper solution (0.01 M) into a conical flask, add 100 mL de-ionised water, 5 mL concentrated ammonia solution and 5 drops of the indicator solution. Titrate with standard EDTA solution (0.01 M) until the colour changes from purple to dark green. 

It should be noted that this method is only applicable to solutions containing up to 25 mg copper ions in 100 mL of water if the concentration of Cu2+ ions is too high, the intense blue colour of the copper(II) ammine complex masks the colour change at the end point. The indicator solution must be freshly prepared. 

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