Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Amber Chang on January 14, 2015, 09:30:58 AM
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Hi, guys,
I want to know how to identify the Calcium ion from a solution which contains both of Calcium ion and Magnesium ion.
I try to use the USP method to identify the Calcium. However, I am afraid the Magnesium salts are also precipitated.
USP method is as follows.
Calcium—Solutions of calcium salts form insoluble oxalates when treated as follows. To a solution of the calcium salt (1 in
20) add 2 drops of methyl red TS, and neutralize with 6 N ammonium hydroxide. Add 3 N hydrochloric acid, dropwise, until
the solution is acid to the indicator. Upon the addition of ammonium oxalate TS, a white precipitate is formed.
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EDTA in pH high enough to precipitate Mg(OH)2.
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Magnesium sulfate is soluble, calcium sulfate isn't.
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Do chelatometric titration:
1st titrate with chelaton III using eriochrome black T in buffered solution (we used 5ml of schwarzenbach buffer) to determine total concentration of Ca and Mg and then titrate with chelaton III using murexide in basic solution (added 5 ml NaOH) to determine amount of Ca.