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Topic: Chelatometry  (Read 2375 times)

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Offline wuutoshi

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Chelatometry
« on: April 21, 2014, 07:18:11 AM »
We are titrating Cu2+ ions (in 0.01M solution of CuSO4 with Chelaton III (sodium salt of EDTA). Metallochromic indicator is murexide which forms weaker yellow complex with Cu2+. After Chelaton has chelated all Cu2+, the solution turns blueish - purplish that corresponds to the free form of murexide.
When approx. 10% of Chelaton remains to add before equivalence point is reached, we are asked to add few drops of NH3(aq). What is the reason of doing this?
My thought about this is that the complex formed with ammonia makes Cu22+ more accessible and thus assures swifter transition to equivalence point (?)

//Hunter2: Ah, it makes sense. Thank you.
« Last Edit: April 21, 2014, 07:37:03 AM by wuutoshi »

Offline Hunter2

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Re: Chelatometry
« Reply #1 on: April 21, 2014, 07:28:59 AM »
It should keep the pH on alkaline side.

Offline billnotgatez

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Re: Chelatometry
« Reply #2 on: April 21, 2014, 03:53:28 PM »
@wuutoshi
you should post in order
you should not modify previous post when responding
Please read forum rules

Quote
//Hunter2: Ah, it makes sense. Thank you.

Offline kriggy

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Re: Chelatometry
« Reply #3 on: April 22, 2014, 01:36:03 AM »
By titrating with chelaton you are lowering pH over time of the analysis, the reaction is
Cu2+ + EDTA  :rarrow: [CuEDTA] + 2H+
The different pH might alter the results so thats why you add the NH3, to neutralize the acidic pH

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