Skill 3-5 : Lactic acid (M = 90.08 g/mol) contains 40.0 mass % C, 6.71 mass % H, and 53.3 mass % O.
(a) Determine the empirical formula of lactic acid.
(b) Determine the molecular formula.
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Plan: Assume 100 g lactic acid to express each mass % as grams. Convert grams to moles and find the empirical formula.
Solution: Express mass % as grams; assume 100 g lactic acid:
Similarly, there are 6.71 g H and 53.3 g O.
Converting from grams of elements to moles:
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