<P> The precipitation method is the one used for the determination of the amount of calcium in water . Using this method, an excess of oxalic acid, H C O, is added to a measured, known volume of water . By adding a reagent, here ammonia, the calcium will precipitate as calcium oxalate . The proper reagent, when added to aqueous solution, will produce highly insoluble precipitates from the positive and negative ions that would otherwise be soluble with their counterparts (equation 1). </P> <P> The reaction is: </P> <P> Formation of calcium oxalate: </P> <P> Ca (aq) + C O → CaC O </P>

Principle of determination of calcium ion content of a solid sample by gravimetric analysis