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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: GreenHorn on January 30, 2007, 08:50:49 AM

Title: EDTA Titration with Calcium Chloride
Post by: GreenHorn on January 30, 2007, 08:50:49 AM

Hi guys, just wondering... I was having this problem with titrating (50ml burette) a 0.01moldm3

Sodium salt of EDTA into a 50ml solution of 0.01moldm3 Calcium Chloride. The pH was kept

constant at 10 using 3 drops of ammonium chloride and Eriochrome Black T indicator solution

was added. The solution was supposed to turn from red to blue but wouldnt! After a while I

tried halving the volume of Calcium Chloride solution to 25ml solution. This worked, the solution

then turned from red to blue, but i don't know why only after i halfed the volume of CaCl...

Any ideas? I have to explain why in an evaluation. Ta in advance.

Title: Re: EDTA Titration with Calcium Chloride
Post by: Borek on January 30, 2007, 11:42:47 AM

Think about reaction stoichiometry.

Title: Re: EDTA Titration with Calcium Chloride
Post by: GreenHorn on January 31, 2007, 10:52:23 AM

Call me stupid but i just don't see it?

Title: Re: EDTA Titration with Calcium Chloride
Post by: Borek on January 31, 2007, 11:06:25 AM

At what molar ratio do the EDTA and Ca²⁺ react?

How much of both do you use?

When does the color change?

Title: Re: EDTA Titration with Calcium Chloride
Post by: GreenHorn on February 13, 2007, 12:19:47 PM

Ok for one of the results the titre was 20ml for EDTA and it reacted with 25cm3 of the CaCL in the conical flask, the moles react 1 to 1.

The colour changed after 20ml of EDTA was titrated into the water sample. This worked.

Previously, i could not obtain a result as the CaCl solution would not turn colour. But i was using 50ml of CaCl in the conical flask instead of 25ml. No matter how much EDTA i added the solution would not turn colour.

Title: Re: EDTA Titration with Calcium Chloride
Post by: Borek on February 13, 2007, 12:44:47 PM

For the color change you have to add small excess of EDTA so that all Ca²⁺ is complexed. Calculate if your combination of volumes/concentrations/burette size allows for that if you use 50 mL of calcium solution.