Sm Digital Resources for Chemistry 11/26/17 CH07 Required HW This is a Chemical

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Sm Digital Resources for Chemistry 11/26/17 CH07 Required HW This is a Chemical Equation question/It is worth 1 point/You have 7 of 7 attempts remaining/There is no attempt per a See page 299 15 Question (1 point) A compound containing only C. H, and O, was extracted from the bark of the sassafras tree. The combustion of 31.1 mg produced 84.4 mg of Co2 and 173 mg of H20. The molar mass of the compound was 162 g/mol. Determine its empirical and molecular formulas v 1st attempt Part 1 (0.5 point) see Periodic Table Note that formulas of organic compounds should first list the carbon and hydrogen with the rest of the atoms listed in alphabetical order. For this problem use the format: CyHyOp where x y and z are subscripts of 2 or greater Empirical Formula: Part 2 (0.5 point) see Hint Molecular Formula:

Explanation / Answer

C%    = 12*wt of Co2*100/44* wt of compound
         = 12*84.4*100/44*31.1   = 74%
   H%     = 2*wt of H2O *100/18*wt of compound
          = 2*17.3*100/18*31.1   = 6.18%
   O%    = 100-(C%+ H%)
         = 100-(74+6.18)   = 19.82%

Element        %        A.wt    relative number     simple ratio
C              74       12         74/12 = 6.16      6.16/1.24 = 5
H              6.18      1        6.18/1 = 6.18     6.18/1.24 = 5
O              19.82    16        19.82/16 = 1.24    1.24/1.24 = 1
   The empirical formula of the compound = C5H5O
The empirical formula weight    = 12*5 +1*5 + 16 = 81g/mole
molecular weight = 162g/mole
molecular formula = (empirical formula)n
              n      = M.Wt/E.F.Wt
                     = 162/81 = 2
The molecular formula = (C5H5O)2 = C10H10O2

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