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Back to Percent Composition by Mass Empirical formula is the smallest whole number ratio of moles of each element in a compound. CaCl
Level 1 What is the empirical formula of the following compounds? (so reduce the formula if you can)
Level 2
If you have %. Assume the mass to be 100g, so the % becomes grams.
Examples-Caffeine has an elemental analysis of 49.48% carbon, 5.190% hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a molar mass of 194.19 g/mol. What is the molecular formula of caffeine? (Hint-Save the molar mass 194.19g/mol until the end)
49.48% C, 5.190%H, 16.47% O and 28.85% N Step 1 Mass is 100% so % becomes grams 49.48g C, 5.190gH, 16.47g O and 28.85g N Step 2 determine the moles of each element 49.48g C x (12.0 g C / mole) = 4.123moles C Step 3 determine the mole ratio by dividing each elements number of moles by the smallest Dividing by the smallest (1.029) we get Step 4 Double, triple .. to get an integer is they are not all whole numbers The values are all really close to whole numbers. Empirical Formula= C Example- Molecular Formulas (Steps 5-7) It has a molar mass of 194.19 g/mol. Step 5 After you determine the empirical formula, determine its mass. Empirical Formula= C (4 carbon x 12.0) + (5 hydrogens x1.0) + (1 oxygen x 16.0) + (2 nitrogen x 14.0) =97.0g/mol Step 6 Determine how many times greater the molecular mass is compared to the mass of the empirical formula. molecular mass/ empirical formulas mass 194.19g/mol / 97.0g/mol = 2 Step 7 Multiply the empirical formula by this number 2x C better==>
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