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Hi, Our senior chemistry class is analysing water for quality and needs to do the EDTA titration. Does anyone have any tips for dissolving the EDTA and also a good recipe for the eriochrome Black T indicator.

Hi Vera,

Dissolving EDTA is quite difficult as the solution you are dissolving it into must be at the correct pH. Otherwise the solution will not dissolve. The ideal pH for this is around pH 8. This step is included in the method.

The best way to dissolve this is to:

Dissolve about 3.8 g of the dihydrate of the disodium salt (di-Sodium EDTA 2H[sub]2[/sub]O) in approximately 1 L of deionized water in a large beaker using a magnetic stirrer.

A small amount of sodium hydroxide can be added if there is any difficulty in dissolving the EDTA, as the EDTA requires a solution that is around pH 8. Try not to exceed 3.8 g of the disodium salt because much more than this dissolves only with difficulty.

Before use, the EDTA solution should be filtered using a Buchner funnel and suction filtration if this is necessary.

This will equate to 0.01M EDTA Solution

This should get you out of trouble..


Eriochrome Black T.

Eriochrome is a Compleximetric Indicator turning from the Protonated Black/Blue colour to a Red colour when it has complexed with Metal Ions.

Unfortunately Eriochrome Black T is a large complex molecule that cannot be duplicated or made from mixtures. Therefore when it is time to use this it must be purchased as the complex "Eriochrome Black T".

Hope this all helps..

Thanks Robb, That advice will definately help me out.

Hey robb
you forgot to mention that you obtain erichrome black T as a black powder
than dissolve 2g in 150ml of Ammonia solution than add 50ml of ethanol.

EBT 0.5% in ethanol
refer
http://courses.cm.utexas.edu/pmccord/sp ... Wk4Lab.pdf water testing Yr12 Chem
this is an excellent PDF dealing with the prac and its methodology