EMPIRICAL FORMULA AND MOLECULAR FORMULA

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EMPIRICAL FORMULA AND MOLECULAR FORMULA UNIT #6 STOICHIOMETRY

Background Sometimes you might be asked to find the chemical formula of compound given its percent composition. Steps: 1) Convert the percents of elements to grams. 2) Convert to moles 3) Divide by the lowest number of moles 4) Determine the empirical formula In order to determine the molecular formula, divide the molar mass of the molecular formula by the molar mass of the empirical formula and multiply the subscripts of the empirical formula by this number.

Example A compound contains 71.65% Cl, 24.27% C, and 4.07% H. Its molar mass is 98.96 g/mol. Determine the empirical formula and chemical formula.

Example A compound is found to contain 31.42 % sulfur, 31.35 % oxygen, and 37.23 % fluorine by weight. Its molar mass is 102.2 g/mol. Determine the empirical formula and molecular formula.

Example A compound contains 57.54% C, 3.45% H, and 39.01% F. Its molar mass is 438.32 g/mol. Determine the empirical formula and molecular formula.

Challenge Problem The combustion of 1.50 grams of a hydrocarbon resulted in 4.40 grams of CO2 and 2.70 grams of H2O. Determine the empirical formula of the hydrocarbon. The molar mass of the hydrocarbon is found to be 78 g/mol. What is its molecular formula?