Percent Composition by mass

Definition The percent by mass of each element in a compound

Percent by Mass Mass (g) element × 100 Mass (g) compound **Round each percent to the hundredths place

Steps Find the molar mass of your compound Find the percent composition of each element by using the equation To check your work, the percent's should add up to 100% exactly, if not go back and check your work

Molar Mass of Compound Al = 26.98g Example Determine the percent composition of each element of aluminum chloride, AlCl3 %Al = 26.98g 133.33g × 100 = 20.24 % Al Molar Mass of Compound Al = 26.98g + Cl = 35.45g × 3 133.33g %Cl = 35.45g x3 133.33g × 100 = 79.76 % Cl

Example Determine the percent composition of each element of H2SO4? (What is its name?)

Example Determine the percent composition of each element of Ca(OH)2 (What is its name?)