05_Empirical_and_Molecular_Formulas - Empirical and...

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Empirical and Molecular FormulasOnce a scientist has determined the percent composition of the various elements in the samplethe empirical formula can then be determined.The empirical formula represents the smallestwhole-number ratio of the elements in the compound.When determining the empirical formulaalways assume that you have a 100-gram sample; therefore the percent composition of eachelement can be used as the number of grams that you have of each element.There are three steps in determining the empirical formula of a compound:Step 1:Change the number of grams given to moles by using the atomic mass of eachelement. Use at least 4 significant figures!Step 2:Determine the mole ratio by dividing each number of moles by the smallestnumber of moles.If this does produce whole number ratios of moles, multiply allmole ratios by a whole number so that you do have whole numbers.Step 3:Use the ratio as subscripts in the formula.The elements usually appear in theproblem in the same order that they should appear in the formula.Example 1:A compound is 12.69% aluminum, 19.73% nitrogen, and 67.57% oxygen.Whatis the empirical formula of the sample?Al(NO)Aluminum Nitrate₃ ₃Example 2:A 250.0 g sample of a compound contains 171.0 grams of chromium and theremainder is oxygen. Calculate the empirical formula of this compound.

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Term
Fall
Professor
NoProfessor
Tags
Molecular Formulas, Empirical and Molecular Formulas, molecular formula Homework

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