Percent Composition

Purpose: We find percent composition using mass. It will show us what % of the molecule is made up of its individual elements. This will become very important when we learn how to find formulas in the near future.

Steps for Percent Composition Find the Molar Mass (if applicable). Divide each elements’ mass by the total compound mass. Multiply each by 100 to get a percent.

Sample Problem #1 An unknown compound has a mass of 370.0 g. Upon analysis, chemists find that the sample contains 150.0 g of carbon, 180.0 g of oxygen and 40.0 g of hydrogen. What is the percent composition of each element in the compound? C: 150.0 g / 370.0 g =.4054 x 100 = 40.54 % O: 180.0 g / 370.0 g = .4865 x 100 = 48.65 % H: 40.0 g / 370.0 g = .108 x 100 = 10.8 %

Sample Problem #2 Calculate the percent composition of each element in the following compound: Silver Nitrate AgNO3 Total mass= 170g Ag-108/ 170=.4248 x 100 = 63.53% N- 14/ 170=.05517 x 100 = 8.24% O- 48/ 170= .50409 x 100 = 28.23% ____________ 100%