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2.3.5: Empirical and Molecular Formulas (Problems)

  • Page ID
    210642
  • PROBLEM \(\PageIndex{1}\)

    Determine the empirical formulas for compounds with the following percent compositions:

    (a) 15.8% carbon and 84.2% sulfur
    (b) 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen

    Answer a

    CS2

    Answer b

    CH2O

    PROBLEM \(\PageIndex{2}\)

    Determine the empirical and molecular formula for chrysotile asbestos. Chrysotile has the following percent composition: 28.03% Mg, 21.60% Si, 1.16% H, and 49.21% O. The molar mass for chrysotile is 520.8 g/mol.

    Answer

    Mg3Si2H3O8 (empirical formula), Mg6Si4H6O16 (molecular formula)

    PROBLEM \(\PageIndex{3}\)

    Polymers are large molecules composed of simple units repeated many times. Thus, they often have relatively simple empirical formulas. Calculate the empirical formulas of the following polymers:

    (a) Lucite (Plexiglas); 59.9% C, 8.06% H, 32.0% O
    (b) Saran; 24.8% C, 2.0% H, 73.1% Cl
    (c) polyethylene; 86% C, 14% H
    (d) polystyrene; 92.3% C, 7.7% H
    (e) Orlon; 67.9% C, 5.70% H, 26.4% N

    Answer a

    C5H8O2

    Answer b

    CHCl

    Answer c

    CH2

    Answer d

    CH

    Answer e

    C3H3N

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    PROBLEM \(\PageIndex{4}\)

    A major textile dye manufacturer developed a new yellow dye. The dye has a percent composition of 75.95% C, 17.72% N, and 6.33% H by mass with a molar mass of about 240 g/mol. Determine the molecular formula of the dye.

    Answer

    C15H15N3

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