May 31, 2020, 03:17:11 AM
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### Topic: Lack of colour change in titration for standardising EDTA (Eriochrome Black T)  (Read 185 times)

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#### TheSimpliFire

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##### Lack of colour change in titration for standardising EDTA (Eriochrome Black T)
« on: February 05, 2020, 03:19:45 PM »
I am currently following this method to standardise my $0.01\ce M$ EDTA solution. As instructed, I have added

- $10\ce{cm^3}$ of the buffer solution ($7\ce g$ of $\ce{NH4Cl}$ with $57\ce{cm^3}$ conc. ammonia) and

- $1\ce{cm^3}$ eriochrome black T solution ($0.2\ce g$ indicator with $15\ce{cm^3}$ conc. ammonia and $5\ce{cm^3}$ ethanol)

to $10\ce{cm^3}$ of EDTA which made a blue-black solution.

However, during the titration with $0.025\ce M$ $\ce{MgCl2}\,(\ce{aq})$, there was no colour change (stayed blue-black) except for some red bubbles on top of the solution. This is clearly not in accordance with the supposed reaction given in Figure $1$ of the link as the colour changes from blue to pink.

The only thing I can think of is that in the method, $0.05\ce M$ EDTA solution was used instead of $0.01\ce{M}$. Would this have caused the lack of colour change, or something else?

#### Borek

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##### Re: Lack of colour change in titration for standardising EDTA (Eriochrome Black T)
« Reply #1 on: February 05, 2020, 05:55:31 PM »
Way too much indicator IMHO. Try a single drop (or even a drop of a less concentrated solution).
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### TheSimpliFire

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##### Re: Lack of colour change in titration for standardising EDTA (Eriochrome Black T)
« Reply #2 on: February 08, 2020, 06:33:47 AM »
1 drop worked, thanks!