| Stepwise Complexometric Determinations of Calcium
and Magnesium in Lime and Magnesia
Bearing Materials |
S. DASGUPTA, B. C. SINHA AND N. S. RAW AT*
Pages : 14-16
DOI : 10.1080/0371750X.1982.10822561 |
| Abstract |
| A simple and rapid complexometric method for stepwise titration of
calcium and magnesium, when present in unfavourable ratios, has
been successfully worked out. The method is based on the direct
titration of calcium of pH 12 with EDTA, using thymolphthaleincalcein
indicator. The adsorption of metallochromic indicator and
any Cat+ has been prevented by the prior addition of titan yellow
which masks magnesium by lake formation. Glycerine is also added
as a protective colloid to stabilize the lake and to prevent coprecipitation
of Ca(OH)2 • After dissolution of the lake in HCl acid, subsequent
addition of ascorbic acid, then ammonia and ammonia buffer, for
controlling the pH at 10, Mg is determined in the same aliquot by
direct titration with EDTA using Eriochrome Black T indicator. The
method has been successfully applied for the determination of calcium
oxide and magnesium oxide in magnesite, dolomite, asbestos and
other lime and magnesia bearing materials. |
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