You assume a 100 g sample, and the masses are then numerically the same as the percentages.
Are you talking about empirical formula calculations, where you have to convert the percentages to masses?
For example, a compound may contain 50.05 % sulfur and 49.95 % oxygen by mass.
You first have to convert these percentages to masses.
You should assume a total mass of exactly 100 g.
In mathematics, a percentage is a decimal fraction.
##”Decimal Fraction” = %/100##
So, 40.05 % = 0.4005, and 49.95 % = 0.4995
To get the mass, you multiply the total mass by the decimal fraction.
Mass of S = 0.4005 × 100 g = 40.05 g. Mass of O = 0.4995 × 100 g = 49.95 g
If you use conversion factors in your chemical calculations, you can write
##”Mass of S” = cancel(“100 g sample”) × “40.05 g S”/cancel(“100 g sample”) = “40.05 g S”##
##”Mass of O” = cancel(“100 g sample”) × “49.95 g O”/cancel(“100 g sample”) = “49.95 g O”##
Either method is quite acceptable. Use the one that you prefer.
