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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: micky on March 07, 2018, 01:41:07 PM

Title: Determination of the content of a mixture of solid materials
Post by: micky on March 07, 2018, 01:41:07 PM
Hello everyone!

Does anyone of you know how to determine the content of EACH compound in the mixture: CaCO3, Ca(OH)2 and a moisture?

If someone does, I'd love you to explain me how to do it :)
Title: Re: Determination of the content of a mixture of solid materials
Post by: Borek on March 07, 2018, 01:53:39 PM
You have to show your attempts before receiving help, this is a forum policy.

Many ways to skin that cat, depending on what you know, so there is no one, general answer.
Title: Re: Determination of the content of a mixture of solid materials
Post by: micky on March 07, 2018, 03:02:44 PM
I'm not sure whether it is a good way but I would use acid-base titration using two indicators. I'd take hydrochloric acid with phenolphthalein and I could titrate calcium hydroxide and calcium carbonate and next I can add methyl orange and continue the titration of the remaining part of CaCO3. Nevertheless, like I said it is just my wild guess.
Title: Re: Determination of the content of a mixture of solid materials
Post by: Arkcon on March 07, 2018, 04:09:11 PM
You have guess upon the typical method.  There may be others depending on how many sample you have, and to what level you need the answer.  There is also a quite famous titration method for moisture.  Its a tricky procedure, using specialized equipment, and again, we need to know -- how good of an answer do you need and why, and what your technical level is.
Title: Re: Determination of the content of a mixture of solid materials
Post by: micky on March 08, 2018, 01:24:08 AM
Okay. I've got both CaCO3 and Ca(OH)2 in the amount of macro (quite a lot). I think the best way to determine the contents is by using a classic analysis (titrations etc.) Is there any better classical way to determine it (than the one I have mentioned)? If not, how should I start the procedure of determining it in the way I've mentioned? Should I dissolve CaCO3 and Ca(OH)2 first in something? If yes, what should I dissolve it in?
Title: Re: Determination of the content of a mixture of solid materials
Post by: Borek on March 08, 2018, 03:41:32 AM
CaCO3 solubility is quite low (Ksp around 3×10-9), so while the Warder method sounds plausible in principle, it will be probably impossible to do.

I would try total calcium (after dissolving sample in HCl) and separately Ca(OH)2 in filtrate.
Title: Re: Determination of the content of a mixture of solid materials
Post by: micky on March 08, 2018, 12:09:05 PM
But how can you separate Ca(OH)2 from CaCO3? Both of them after dissolving will be in a solution.
Title: Re: Determination of the content of a mixture of solid materials
Post by: Corribus on March 08, 2018, 12:29:52 PM
I would use thermogravimetric analysis. Your components decompose at significantly different temperatures.
Title: Re: Determination of the content of a mixture of solid materials
Post by: Borek on March 08, 2018, 02:13:53 PM
Quote from: micky on March 08, 2018, 12:09:05 PM
But how can you separate Ca(OH)2 from CaCO3? Both of them after dissolving will be in a solution.

Ca(OH)2 is much more soluble, so - if the sample mass and volume are carefully selected - it can be possible to dissolve just the hydroxide, leaving CaCO3 as a solid; I can be wrong though.