Talc is a magnesium containing mineral commonly found in soapstone. You have a 15.0g sample of soapstone and you completely dissolve in solution. A 10.0 mL fraction of that solution is added to a 250 mL volumetric flask and diluted to the mark with 8-hydroxyquinoline solution to form a magnesium complex which precipitates (reaction shown below). If you collect 631 mg of complex, what was the % mass of talc in the soapstone?
Mg2++ 2C9H7NO --> Complex + 2H+