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Percent Composition. Vocabulary Percent Percent Composition. “No. 5” Mark Rothko Russian 1960. prior knowledge. How could you calculate what percentage of the painting is red, what percentage is black, and what percentage is green?. General Formula for Percent. Percent Composition.
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Percent Composition • Vocabulary • Percent • Percent Composition “No. 5” Mark Rothko Russian 1960
prior knowledge • How could you calculate what percentage of the painting is red, what percentage is black, and what percentage is green?
Percent Composition • Chemists often need to know the percentage of each element in a compound by mass. This is called percent composition.
Example 1 To the right are pictures of copper(II) chloride, CuCl2. If a 34.2 g sample of copper(II) chloride contains 16.2 g of copper and 18.0 g of chlorine, what is the percent composition of CuCl2?
Example 1 Continued • First, determine the percent of copper in the compound: • Next, determine the percent of chlorine in the compound:
Example 2 • What is the percent composition of lithium nitrate? • First we need its formula: • LiNO3 • Notice we don’t have any masses in this problem. Any ideas on what we can use to solve for the percent composition?
Example 2 Continued • We’ll use the molar masses of everything rather than the mass! • Li: 6.94 g/mol • N: 14.01 g/mol • O: 16.00 g/mol • LiNO3: 68.95 g/mol
Example 2 Continued 100.0%