Percent Composition Chapter 7-3, p. 221 - 228

Formula Mass Defined as: the sum of the average atomic masses of all the atoms represented in the chemical formula of a molecule, ionic compound or ion. ***This is the same as the molar mass you learned to compute in Chapter 3!

Example CO2 = carbon dioxide 1 C = 1(12.01 g/mol) = 12.01 g/mol 2 O = 2(16.00 g/mol) = 32.00 g/mol Total formula mass = 44.01 g/mol

Example KClO3 = potassium chlorate 1 K = 1(39.10 g/mol) = 39.10 g/mol 1 Cl = 1(35.45 g/mol)= 35.45 g/mol 3 O = 3(16.00 g/mol) = 48.00 g/mol Total formula mass =122.55 g/mol

Example (NH4)2SO3 = ammonium sulfite 2 N = 2(14.01 g/mol) = 28.02 g/mol 8 H = 8(1.01 g/mol) = 8.08 g/mol 1 S = 1(32.07 g/mol) = 32.07 g/mol 3 O = 3(16.00 g/mol) = 48.00 g/mol Total formula mass =116.17 g/mol

Percent Composition Defined as: the percentage by mass of each element in a chemical compound For example, the amount of oxygen contained in one unit of NaOH by mass is 32.6% So we would state that NaOH is 32.6% oxygen; this is the percent composition of oxygen in NaOH

Example CO2 = carbon dioxide 1 C = 1(12.01 g/mol) = 12.01 g/mol 2 O = 2(16.00 g/mol) = 32.00 g/mol Total formula mass = 44.01 g/mol Now find the percent composition of oxygen… take the mass and divide by the total, times 100%… 32.00/44.01 g/mol X 100% = 72.71%

Example KClO3 = potassium chlorate 1 K = 1(39.10 g/mol) = 39.10 g/mol 1 Cl = 1(35.45 g/mol)= 35.45 g/mol 3 O = 3(16.00 g/mol) = 48.00 g/mol Total formula mass =122.55 g/mol Now find the percent composition of oxygen… take the mass and divide by the total, times 100%… 48.00/122.55 g/mol X 100% = 39.17%

Example (NH4)2SO3 = ammonium sulfite 2 N = 2(14.01 g/mol) = 28.02 g/mol 8 H = 8(1.01 g/mol) = 8.08 g/mol 1 S = 1(32.07 g/mol) = 32.07 g/mol 3 O = 3(16.00 g/mol) = 48.00 g/mol Total formula mass =116.17 g/mol Now find the percent composition of oxygen… take the mass and divide by the total, times 100%… 48.00/116.17 g/mol X 100% = 41.32%

You Try It! Percent composition of P and Br in PBr5 P=7.19%; Br=92.81% Percent composition of Ag and O in Ag2O Ag=93.10%; O=6.90% Percent composition of C, H, and O in C6H12O6 C=39.99%; H=6.73%; O=53.28% What is the percent composition of sugar in a piece of bubble gum?