A sample of a substance containing only magnesium and chlorine was tested in the laboratory and was found to be composed of 74.5% chlorine by mass. If the total mass of the sample was 190.2 grams, what was the mass of the magnesium?
In a binary compound,
So we take that figure and multiply it by the mass of the sample to give under
Note that you could use the data given to give an empirical formula for the compound.