10.3. Chemical Formulas http://www.ck12.org
FIGURE 10.4
Foods like peanut butter provide nutritional information on the label in the form of masses of different types of
compounds present per serving.Percent Composition and Mass
Determining Percent Composition from Mass Data
We can calculate percent composition based on the following formula:
% by mass=mass of compoundmass of element ×100%The example below shows how the percent composition of a compound can be calculated based on mass data:
Example 10.13
A certain newly synthesized compound is known to contain the elements zinc and oxygen. When a 20.00 g sample
of the compound is decomposed, 16.07 g of pure zinc remains. Determine the percent composition of the compound.
Answer:
If the compound contained only zinc and oxygen, and 16.07 grams was due to the zinc, we can subtract to determine
the mass of oxygen in the original sample:
Mass of oxygen = 20.00 g –16.07 g = 3.93 g O
Then, we divide the individual masses of each element by the total mass of the sample to determine the percent (by
mass) of each element in the compound: