Learn the procedure for making eriochrome black T indicator solution.
The compound that changes color when exposed to acidic or basic solutions is called an indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint/equivalence point.
Eriochrome Black T/ solochrome black-T (C20H12N3NaO7S) is an azo dye used in complexometric titrations as an indicator. This blue dye also forms a complex with calcium and magnesium ions, turning pink in the process.
Mordant Black II comes in blue powder form which is soluble in water and alcohol, and insoluble in common organic solvents. It is mostly employed as an indicator in the ethylenediaminetetraacetic acid (EDTA) method for determining the hardness of the water.
How to prepare eriochrome black T indicator for titration:
- Weigh accurately 0.5 gm of eriochrome black-T/solochrome black-T and pour it into a 100.00 ml volumetric flask containing 50.00 ml of ethyl alcohol and swirl until it completely dissolved.
- Weigh 4.5 gm of hydroxylamine hydrochloride and transfer it to the flask containing the EBT and swirl until it completely dissolved.
- Once it is dissolved, dilute to 100.00 ml with ethyl alcohol.
- The concentration of the prepared solution is about 5 g/L.
Eriochrome black T has two pKa values, 6.3 and 11.55. Its ph range is 7.0 to 11.0. It transitions from blue to pink through the pH range and is used as a pH indicator (Metal indicator).
It is blue in its deprotonated state. When it forms a complex with magnesium, calcium, or other metal ions, it turns red. The indicator is added and remains blue because EDTA contains all Ca2+ and Mg2+ ions.
References:
- Wikipedia contributors. (2022, January 17). Eriochrome Black T. In Wikipedia, The Free Encyclopedia. Available Here:
- ‘Eriochrome Black T Solution Preparation’. Sciencing, Available Here:
- Law.resource.org. 2022. [online] Available Here:
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