UNIT 5B PERCENT COMPOSITION X 100= % mass of element mass of element mass of compound part whole X 100

The relative amounts of the elements in a compound are expressed as percent composition.

Propane(C 3 H 8 ), is the fuel commonly used in gas grills. Calculate the percent composition of propane. KNOWNS REMEMBER: part whole  Mass of C in propane  Mass of H in propane  Molar mass of propane CALCULATE % C = g C__ g C 3 H 8 = = 81.8% C % H = g H___ g C 3 H 8 = = 18% H X 100 PERCENT COMPOSITION FROM A FORMULA C: 12.0g x 3 = 36.0g H: 1.0g x 8 = 8.0g 44.0g/mol C 3 H 8 X 100

Try this... Find the percent composition of water. KNOWN  Formula of water  Mass of hydrogen in water  Mass of oxygen in water CALCULATE % H = =X % H % O = X 100= 88.9 % O PERCENT COMPOSITION FROM A FORMULA H2OH2O H: 2(1.0g) = 2.0g O: 1(16.0g) = 16.0g REMEMBER: part whole X g/mol H 2 O

Find the % composition of barium carbonate. BaCO 3 Ba C O x 1 = 137.3g/mol 12.0 x 1 = 12.0g/mol 16.0 x 3 = 48.0g/mol 197.3g/mol /197.3 x 100 = 69.59% 6.08% 24.3% Molar mass Divide by the total and multiply by 100

PERCENT COMPOSITION FROM MASS DATA When a g sample of a compound containing only Mg & O is decomposed, 5.40 g of O is obtained. What is the % comp. of this cmp? KNOWN  compound = g  oxygen = 5.40 g  magnesium = ? 13.60g – 5.40 g = 8.20 g Mg CALCULATE % Mg = X 100 = 60.3 % Mg % O = X 100 = 39.7 % O REMEMBER: part whole X 100 If you are not given the mass of each of the elements, SUBTRACT to find them!

PERCENT COMPOSITION FROM MASS DATA Try this... A 34.0 g sample of a compound containing 8.5 g of O is formed. The remaining portion is composed of Ca. What is the % composition of this compound? KNOWN 25% oxygen 75.0% calcium compound = 34.0 g oxygen = 8.5 g calcium = ? 34.0g – 8.5 g = 25.5 g Ca CALCULATE REMEMBER: part whole REMEMBER: If you are not given a mass for each of the elements, SUBTRACT to find them! X 100