Complexometric titration or chelatometry is a method of volumetric analysis in which the colored complex is used to determine the endpoint of the reaction. Complexometric titrations using EDTA are based on the fact that many metallic ions form stable complexes with this tetradentate ligand.
The amount of hard water cations in water is measured as 'hardness.' Calcium, magnesium, zinc, iron, and other polyvalent metal ions are among the hard water cations. The main contributors to the water hardness in most samples are Ca2+ and Mg2+ ions. Titration with the complexing agent EDTA is a simple way to quantify calcium and magnesium. Temporary hardness and permanent hardness are the two types of hardness.
Why does the steel blue color of the EBT indicator change into a wine red color when added to hard water?
At pH 10, EBT turns blue in a buffer solution which is an aqueous solution containing a weak acid and its conjugate base, or vice versa. When calcium ions are added, it turns red. The ions that cause water hardness, such as calcium, and magnesium turn the EBT indicator from steel blue to wine red.
Why a blue color appears at the endpoint in the hardness determination experiment by EDTA?
Eriochrome Black T has a loosely binding to metal ions, whereas EDTA has a significant binding to metal ions. When all metal ions are bound to Ethylenediaminetetraacetic acid, the indicator EBT in the sample remains free and the solution appears blue.
What happens when EBT is added to hard water?
When the eriochrome black T (EBT) indicator is applied in the sample of hard water with a pH of about 9 to 10, it produces a wine red colored unstable complex with Ca2+ and Mg2+ ions in the sample.
What is the reason for the blue color observed at the endpoint in the estimation of the hardness of water?
Additional EDTA removes the magnesium ions from the Eriochrome black-T indicator after all free calcium and magnesium have been bound by EDTA, restoring it to its uncomplexed blue color, and an endpoint is determined.
How is EDTA used to measure the hardness of water?
The presence of calcium ions and magnesium ions in water causes hardness. At a specific pH, EDTA interacts quantitatively with the ions. As a result, the ions and hence the hardness can be measured using eriochrome black-T and hence the hardness.
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