Determination of iron III direct titration

Procedure. Prepare the indicator solution by dissolving 1 g variamine blue in 100 mL de-ionised water as already pointed out (Section 10.48), variamine blue acts as a redox indicator. 

Pipette 25 mL iron(III) solution (0.05M) into a conical flask and dilute to 100 mL with de-ionised water. Adjust the pH to 2-3 Congo red paper may be used — to the first perceptible colour change. Add 5 drops of the indicator solution, warm the contents of the flask to 40 °C, and titrate with standard (0.05M) EDTA solution until the initial blue colour of the solution turns grey just before the end point, and with the final drop of reagent changes to yellow. 

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

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