Precipitation Followed by Titrimetric Determination of Calcium

When the precipitated calcium oxalate is dissolved in hot dilute sulphuric acid, the oxalic acid liberated can be titrated against standardised permanganate. 

Ba ions in solution, which is buffered by CH3COOH/CH3COONH4, are precipitated by the addition of (NH4)2Cr04 solution, prepared by adding NH3 to (NH4)2Cr207 solution. 

Dissolve 10 g purest (NH4)2Cr207 in 100 cm HjO and add filtered dilute NH3 solution until the solution is clearly yellow and distinctly alkaline ( 40 cm will be required). When this solution is heated, it should be maintained clearly yellow and distinctly alkaline (if necessary) by further addition of dilute NH3 solution. 

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