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Scan_Doc0097

# Scan_Doc0097 - Formula from Empirical Formula • Obtain...

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n, the atoms ~15N3' e al- t can - . To ula, - ers very close to whole numbers, -- as 9.92 and 1.08, should be ed to whole numbers. Numbers -- as 2.25, 4.33, and 2.72 should not nded to whole numbers. 3.7 Determining the Formula of a Compound 93 PROBLEM-SOLVING STRATEGY Empirical Formula Determination • Since mass percentage gives the number of grams of a particular element per 100 grams of compound, base the calculation on 100 grams of compound. Each percent will then represent the mass in grams of that element. • Determine the number of moles of each element present in 100 grams of compound using the atomic masses of the elements present. • Divide each value of the number of moles by the smallest of the values. If each resulting number is a whole number (after appropriate rounding), these numbers represent the subscripts of the elements in the empirical formula. • If the numbers obtained in the previous step are not whole numbers, multiply each number by an integer so that the results are all whole numbers. PROBLEM-SOLVING
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Unformatted text preview: Formula from Empirical Formula • Obtain the empirical formula. • Compute the mass corresponding to the empirical formula. • Calculate the ratio Molar mass Empirical formula mass • The integer from the previous step represents the number of empirical formula units in one molecule. When the empirical formula subscripts are multiplied by this integer, the molecular formula results. This procedure is summarized by the equation: . . molar mass Molecular formula = (empirical formula) x ---------empirical formula mass XAMPLE 3.10 Determine the empirical and molecular formulas for a compound that gives the following percentages on analysis (in mass percents): 7l.65% Cl 24.27% C 4.07% H The molar massis known to be 98.96 g/mol. Solution Where are we going? • To find the empirical and molecular formulas for the given compound What do we know? ./ Percent of each element ./ Molar mass of the compound is 98.96 glmol...
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