Chrominfo: Complexometric titration procedure

Learn the complexometric titration procedure used to estimate the hardness of water by the EDTA method.

Titration is a typical quantitative chemical analysis method used in laboratories to determine the concentration of an identified analyte in a given sample solution. Titration is classified into four different types namely acid-base titration, redox titration, precipitation titration, and complexometric titration.

Complexometric titrations are used to determine the concentration of metal ions in sample solutions. Complexometric titration is a type of volumetric method that depends on the formation of a complex between the analyte and the titrant. They generally required the use of complexometric indicators that produce weak complexes with analysis.

Procedure for complexometric titration using EDTA:

Aim:

To determine the amount of total hardness of a given water sample by complexometric titration using EDTA.

Requirements:

Pipette, beaker, conical flask, burette, burette stand, wash bottle, funnel, spatula, eriochrome black T indicator, buffer solution, inhibitor, and standard EDTA Solution (0.01M), etc.

Principle:

The presence of dissolved calcium and magnesium salts in water causes hardness, which is unsuitable for drinking, washing, swimming, and also produces the scales in boilers. Hence, the amount of hardness-producing compounds contained in the water sample must be determined.

The total hardness of water is determined by titrating the sample against EDTA using the indicator of Eriochrome Black-T. Indicator produces a weak EBT Ca2+/Mg2+ wine red colored complex with the Ca2+/Mg2+ ions present in the sample solution. In the presence of ammonia buffer which is a mixture of ammonium chloride and ammonium hydroxide at pH 10, the Ca2+/Mg2+ ions preferentially produce a stable EDTACa2+/Mg2+ complex with EDTA, leaving the Eriochrome Black-T free indicator in solution, which is steel blue in color.

Procedure:

Clean and dry all of the equipment.
Keep the burette filled with EDTA solution.
Using the pipette take 25ml of the given sample and 01 ml of buffer solution in a conical flask.
Add 1ml of the inhibitor to the mixture of sample and buffer solution.
Now add 2 drops of Eriochrome Black-T indicator to the mixture until the color changes to wine red.
Now start titration of the mixture with the standard EDTA solution.
The change in color from wine red to blue indicates the endpoint or equivalance point.
Repeat the titration three times to obtain three concurrent readings.