Solve gravimetric analysis problems.
Gravimetric analysis determines how much of a target element a sample contains by converting it quantitatively into a pure, weighable compound. The bridge between the weighed precipitate and the analyte is the gravimetric factor: the mass of analyte per unit mass of precipitate, which is the analyte's molar mass times the number of analyte atoms in the formula, divided by the precipitate's molar mass. Determining sulfur as barium sulfate gives a factor of 32.06 over 233.39, or 0.1374.
Gravimetric factor method
factor = (analyte molar mass x atoms per formula) / precipitate molar mass; analyte mass = precipitate mass x factor; percent = analyte mass / sample mass x 100
Because occluded water and mother liquor would be weighed as precipitate and inflate the result. Ignition to constant mass is the standard control, and it is also why the method demands a precipitate that is stable and non-hygroscopic.
Precipitates containing more than one analyte atom. Determining phosphorus as Mg2P2O7 has two phosphorus atoms per formula unit, so the factor is 2 x 30.97 over 222.55.
Because it is a primary method needing no calibration standard — the answer follows from molar masses and a balance. It remains the reference technique for certifying standards and for sulfate, silica and chloride determinations at high accuracy.