Estimation of magnesium by gravimetry
According to the data given in Vogel, it should be
possible to coprecipitate
Mg and Al if the pH is above 9.
Use about
the same quantity of crystals used for the Al estimation. Transfer the
accurately weighed sample into a
beaker, dissolve in water, raise the pH to 9 by
adding ammonia. Heat the solution
and add oxine reagent to the hot solution. Treat
the precipitate as before. The
precipitate is a mixture of Mg(oxinate)2 and Al(oxinate)3.
Knowing the percentage of Al from the
previous experiment, calculate the percentage of
Mg in the sample.