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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Schrödinger on September 29, 2009, 11:54:56 AM

Title: Doubts in qualitative inorganic analysis
Post by: Schrödinger on September 29, 2009, 11:54:56 AM

Why is it that although Mg2+ can be precipitated as carbonate, we don't use that as a test in group 5, which includes Ca, Sr, Ba? (correct me if i've got the facts wrong)

I tried to reason out why but i couldn't come up with any clue. Please help

Title: Re: Doubts in qualitative inorganic analysis
Post by: typhoon2028 on September 29, 2009, 01:16:49 PM

I think MgCO3 will form hydrates

Title: Re: Doubts in qualitative inorganic analysis
Post by: covek11 on September 29, 2009, 02:00:26 PM

Long time ago I tried to precipitate MgCO3 from Mg(NO3)2 + Na2CO3.
I got a faint ppt. That is all.

Title: Re: Doubts in qualitative inorganic analysis
Post by: renge ishyo on September 29, 2009, 07:00:24 PM

It could be because the magnesium cation is so much smaller than the carbonate (CO₃^2-) anion. A poor size match between the cation and the anion makes for weaker bonds. In contrast the other metals you mention are all larger and would match up better with the large anion. Beryllium carbonate (which can form to some extent) isn't used as a test either and the cation there is smaller still.