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How does indicator work during the determination of hardwater using Edta process

How does indicator work during the determination of hardwater using Edta process
 

Grade:12th pass

2 Answers

Yash Patari
askIITians Faculty 2123 Points
2 years ago
dear student,
Thecombined concentration of calcium and magnesium ionsis considered to be the measure of water hardness. The method uses a very large molecule called EDTA which forms a complex with calcium and magnesium ions. ... The indicator is added and remains blue as all the Ca2+ and Mg2+ ions present are complexed with the EDTA.
Navneet jha
63 Points
2 years ago
Eriochrome Black T is commonly used as indicator for the above titration. At pH 10,
Ca2+(aq) ion first complexes with the indicator as CaIn+(aq) which is wine red. As the
stronger ligand EDTA is added, the CaIn+(aq) complex is replaced by the CaY2-(aq)
complex which is blue. The end point of titration is indicated by a sharp colour change
from wine red to blue.
Titration using Eriochrome Black T as indicator determines total hardness due to Ca2+(aq)
and Mg2+(aq) ions. Hardness due to Ca2+(aq) ion is determined by a separate titration at
a higher pH, by adding NaOH solution to precipitate Mg(OH)2(s), using
hydroxynaphthol blue as indicator.

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