Gravimetric Determination of Magnesium

Magnesium ions in its salt solutions can be precipitated as ammonium magnesium phosphate hexahydrate by an excess of a solution of diammonium hydrogen phosphate. The small solubility of the precipitate in water is overcome in presence of ammonia. The precipitate can be washed with ethanol and ether and dried in air or it can be converted to magnesium pyrophosphate by heating in a muffle furnace. 

Repeat using a prepared sintered porcelain crucible for filtration. Proceed as above until the filtrate is chloride free. Then dry the crucible in an oven at 150 C for an hour and then gradually heat in a muffle furnace to 1 lOO C to constant weight. Calculate from each experiment the concentration of magnesium in mol dm . 

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