Explain the principles of the metal ion indicators used in EDTA titration

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Expert Solution

Metal Ion Indicators:

1. There are several methods to determine end point in EDTA titrations. The most common method is to use metal ion indicator.

2. A metal ion indicator is a compound whose color changes when it binds with metal ion

3. For example: analysis of Mg+2 ion

Erichrome Black T common metal ion indicator is added to the Mg+2 to form a red complex. As EDTA is added, it reacts first with free Mg+2 ion and then with the small amount of red colored Mgindicator complex. At this stage the Mg+2 ion unbounded with indicator and Strongly binds with EDTA. So the color of the complex changes with red to blue which indicates end point of the titration.

Mg+2 + erichorme black T (Indicator) (Blue) ----------> Mgindicator complex (red color)

Mg.indicator (red color) + EDTA (colorless) ----------> Mg.EDTA (Colorless) + Indicator (Blue)

Examples of metal ion indicators are Erichrome black T, Blue - Black T, Calcon, Catechol Violet, etc........

queen_honey_blossom answered 1 year ago

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