It helps to know the % of the components in a shirt because they affect how warm it is, whether it will need to be ironed, and how it should be cleaned.

You will learn how the % of the elements in a compound are important in chemistry.

Chemical CompositionUnit 7

% Composition

% by mass = mass of element x 100 total mass

194.20 g/mol

294.20 g/mol

% by mass = mass of element x 100total mass

% O = 5.40 g O x 100 = 13.60 g

39.7% O

% Mg = 8.20 g Mg x 100 = 13.60 g

60.3% Mg

% by mass = mass of element x 100total mass

% C = 36.03 g C x 100 = 44.11 g

81.68% C

% H = 8.08 g H x 100 = 44.11 g

18.32% H

C3H8: 3 (12.01) + 8 (1.01) = 44.11 g/mol

NH3: %N = 14.01 g N x 100 = 17.04 g

82.22% N

NH4NO3: %N = 28.02 g N x 100 = 80.06 g

35.00% N

17.04 g/mol

80.06 g/mol

1. The percent composition of a compound is found by dividing the mass of each element by the ________.

A. moles of each element

B. percent of each element

C. total mass of the compound

D. total number of elements

Quick Quiz!

2. Calculate the percent by mass of carbon in cadaverine, C5H14N2, a stinky compound present in rotting meat.

A. 67.4% C

B. 58.8% C

C. 51.7% C

D. 68.2% C

Quick Quiz.