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Percent composition and mole conversions pt 2 - Notes

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Percent Composition PURPOSE and PROCEDURE To find out the percentage (by mass) of a particular element in a chemical compound. Calculate the molar mass for the compound. Divide the mass of the element you want to find the percentage of by the molar mass of the compound. Write the answer you get from step B in percentage form. Round your percentage to the tenth. EXAMPLES What percent of Cu2O is O? 2 x Cu = 2 x 63.5 = 127.0 g 1 x O = 1 x 16.0 = 16.0 g molar mass = 143.0 grams/mol % O = Part ? Total = 16.0 ? 143 = .1118 x 100% = 11.2% Example What percent of Al2O3 is Al? 2 x Al = 2 x 27.0 = 54.0 g 3 x O = 3 x 16.0 = 48.0 g molar mass = 102.0 grams/mole % Al = Part ? Total = 54 ? 102 = .5294 x 100% = 52.9% Practice - Find the percent composition

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