Lec7 - Lecture 7 Empirical and Molecular Formulas Percent...

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1 Lecture 7 Empirical and Molecular Formulas Percent Composition Can describe compounds by Percentage by Weight of Elements present Mass (g) of element in 100 g of compound Historical Context Modern Context ± Determine chemical formula ± Elemental analysis ( empirical formula ) ± Mass spectroscopy ± Other physical methods
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2 Percent Composition to Empirical Formulas 1. Assume there is 100 g of the sample , so the percent composition will equal the number of grams of each element. 2. Use the molar masses to convert the grams of each element into the moles of each element . 3. Divide the smallest number of moles of an element into the moles of each element present. 4. Convert the fractional ratios into whole numbers by multiplying all the ratios by the same number. 5. The resulting numbers are the subscripts for each element in the empirical formula. 6. Be able to do this in reverse! Example
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This note was uploaded on 09/23/2010 for the course CHEM 131 taught by Professor Wong during the Fall '08 term at SUNY Stony Brook.

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Lec7 - Lecture 7 Empirical and Molecular Formulas Percent...

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