Percentage Composition

What is percentage composition?

The mass of each element in a compound compared to the entire mass of the compound and multiplied by 100 percent is called the percentage composition of the compound.

To calculate percentage composition:

Mass of element Total mass of compound X 100 = %

The percentage composition of a compound tells you the percent of the mass made up by each element of the compound. This can be determined by calculating the molar mass of a given chemical formula.

Calculating percentage composition of a compound:

EX: What is the percentage composition of hydrogen and oxygen in H 2 O?

Formula Mass = H= 2 atoms X 1 amu= 2 amu O= 1 atom X 16 amu= 16 amu 18amu Percentage of Hydrogen = 2.0 g H 2 18 g H 2 O X 100 = 11% Percentage of Oxygen = 16g O 18g H 2 0 X 100 = 89% (CHECK: Percentages should equal 100%.)

Calculating mass of an element in a compound: EX: How many grams of oxygen are in 5 g of H 2 O? __X__ = 16g O 5 g H 2 0 18gH 2 0 (Cross Multiply) 18 x = (16) (5) x = 80 18 x = 4.44 g O

PRACTICE PROBLEMS

KNO 3

H 2 SO 4

C 2 H 5 OH

C 6 H 5 NH 2

What is the percentage of carbon in CO 2 ?

How many grams of carbon are in 25 g of CO 2 ?

Find the percentage composition of a compound that contains 2.63g of carbon, 0.370g of hydrogen, and 0.580g of oxygen in a 3.58g sample of the compound.