World of Chemistry

VII. Calculations based on Formulae

VII-VI. Empirical and Molecular Formulae

  1. Write the empirical formula for each of the following.
    (a)C8H18, octane
    (b)C12H22O11, sugar
    (c)H2S, hydrogen sulfide
    (d)C2H6O2, ethylene glycol (antifreeze)
  2. From the following empirical formulas and the formula masses for each compound, determine their molecular formulas.
    (a)CH3; formula mass= 30.0 amu
    (b)CH2; formula mass= 84.0 amu
    (c)C3H4O3 (Vitamin C); formula mass= 176 amu
  3. Determine the empirical formula for a compound that contains 18.6 g of phosphorus and 14.0 g of nitrogen.
  4. Determine the empirical formula for a compound that contains 35.6 % of phosphorus and 64.4 % of sulfur.
  5. A compound with a molecular mass of 98.0 g/mole was determined to be 24.49 % carbon, 4.08 % hydrogen, and 72.43 % chlorine.
    (a)Determine the empirical formula of the compound.
    (b)Determine the molecular formula of the compound.

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    Rosamaría Fong, Instructor of Chemistry,
    British Columbia Institute of Technology, Burnaby, B.C. Canada.

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Rosamaría Fong, Instructor of Chemistry
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