Chapter 6 Chemical Quantities 6.6 Percent 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 X 100 = % Total mass of compound This calculation can be performed for a chemical with a known formula Or With laboratory data

Percent Composition – From a Chemical Formula Example: Calculate the percent composition of CO2. Step 1: Calculate the molar mass of each element involved. C: 12.01g/mol 2 O: 2 x(16.00g/mol) = 32.0g/mol Step 2: Calculate the total molar mass of compound. M CO2 = 12.01g/mol + 32.0 g/mol = 44.01g/mol Step 3: Determine precentages 12.01 g/mol C x 100 = 27.29 % C 44.01 g/mol CO2 32.00 g/mol O x 100 = 72.71 % O

Learning Check What is the percent composition of lactic acid, C3H6O3, a compound that appears in the blood after vigorous activity?

Solution STEP 1 3C(12.01) + 6H(1.01) + 3O(16.00) STEP 2 36.03 g C + 6.06 g H + 48.00 g O = 90.08 g/mol Step 3: Determine precentages %C = 36.03 g C x 100 = 40.00% C 90.08 g %H = 6.048 g H x 100 = 6.714% H %O = 48.00 g O x 100 = 53.29% O

Learning Check The chemical isoamyl acetate C7H14O2 gives the odor of pears. What is the percent carbon in isoamyl acetate? 1) 7.102 %C 2) 35.51 %C 3) 64.58 %C

Solution 3) 64.58 %C Molar mass C7H14O2 = 7C(12.01) + 14H(1.008) + 2O(16.00) = 130.18 g/mol Total C = 7C(12.01) = g % C = total g C x 100 total g % C = 84.07 g C x 100 = 64.58 % C 130.18 g

From Lab Data 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.

Solution % C = 2.63g × 100 = 73.46% 3.58g % H = 0.370g × 100 = 10.33% % O = 0.580g × 100 = 16.20% Therefore the unknown compound is 73.46% carbon, 10.33 % hydrogen and 16.20% oxygen.