Complexometric Determination of Aluminium

A known excess of EDTA solution is added to an aliquot of the aluminium salt solution, the excess is then titrated against standard zinc sulphate solution. 

Prepare a 0.01 M solution of purest potassium or ammonium aluminium sulphate in a 250 cm volumetric flask. Pipette 25.0 cm of the solution into a conical flask, run from a burette 40.0 cm of standard 0.01 M EDTA solution, add ammonia solution, dropwise with stirring, to bring the pH to 7-8 (use a pH stick to check the pH). Boil for a few minutes, cool and adjust the pH again as before. Add 50 mg of Solochrome black/potassium nitrate mixture and titrate quickly with standard 0.01 M zinc sulphate solution until a wine red end point is reached. Repeat to obtain concordant results. Calculate from the average titre the [AI(III)] in mol dm .  

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