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(6.2) Molecular Formula of a Compound. Chemical Formula. Recall If we know MF, we can easily determine EF. e.g. pentane C 5 H 10 (MF) CH 2 (EF). Chemical Formula. But, given EF can you determine the MF? e.g. CH 2 O (EF) ? (MF) See p269 table 6.1 for possibilities.
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Chemical Formula • Recall If we know MF, we can easily determine EF. e.g. pentane C5H10 (MF) CH2 (EF)
Chemical Formula • But, given EF can you determine the MF? e.g. CH2O (EF) ? (MF) • See p269 table 6.1 for possibilities.
Chemical Formula • Additional information is needed: molar mass (M) of the compound is needed • e.g. CH2O (EF) ? (MF) • from EF M = 30 g/mol • from expt with compound M = 150 g/mol • ratio: 150 g/mol = 5 30 g/mol Therefore: x CH2O C5H10O5 (EF) (MF)ribose 5
Examples - Calculating Molecular Formula from Empirical Formula Using Molar Mass 1. The empirical formula (EF) of hexane C3H7. In an experiment with a mass spectrometer, a chemist determines the molar mass of hexane is 86.2 g/mol. What is the molecular formula (MF)? 2. The EF of an unknown sample is CH2O. In an experiment it is found that the molar mass of the sample is 121 g/mol. What is the molecular formula (MF)?
Homework • Text p279 # 1, 4, 6, 11, 12, 16 • **Quest on Chapter 6 in 4 days!