MCAT Question of the Day: Empirical Formula

3.6.14 Empirical Formula (MCAT)

Great work on today’s question!

The empirical formula of a compound is the simplest whole number ratio of the atoms in it, whereas the molecular formula represents the actual whole number ratio of the atoms. The molecular formula is usually a whole number multiple of the empirical formula, although sometimes the empirical and molecular formulas are the same.

Remember going through this question that it is asking for which of the statements are FALSE. Statement I is true. For example, water, H2O, has the same empirical and molecular formula. Statement II is false because it is the molecular formula which is usually whole number multiple of the empirical formula, not the other way around.  Finally, statement III is false. H2O2, hydrogen peroxide, has an empirical formula of HO, so the empirical formula is different from the molecular formula given.  Since statements II and III are incorrect, choice C is the answer we’re looking for!

Stay tuned next week for another question!

  • Vivek

    Shouldn’t C say “II and III only” instead of “II and II only”

  • Patrick Boyle

    Vivek – Yes it should! Thank you for catching that!

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