Topic _4A Stoichiometry and Percent Yield

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					Chem. 1010 Tutorials                                                                              Winter 2009

                         Topic #4A: Stoichiometry and Percent Yield

Practice Problems:

1.      Balance the following chemical equation:      __ CH3OH(g) + __ O2(g)  __ CO2(g) + __ H2O(l)

        For each row of the following table fill in the missing masses.
        i.e. For row 1, if 32.0 g of CH3OH reacted, how much O2 must have reacted? ......how much CO2
        was produced? .......how much H2O was produced?

         CH3OH                         O2                             CO2                         H2O
     (grams reacted)             (grams reacted)                (grams produced)            (grams produced)

         32.0 g
                                       64.0 g

                                                                       22.0 g

                                                                                                   36.0 g

2.      The first step in producing arsenic oxide (As2O3) (used to make pesticides) is to roast an arsenic
        ore such as As2S3 in air:
                 2As2S3(s) + 9O2(g)  2As2O3(s) + 6SO2(g)
        How many grams of SO2 (an air pollutant) are produced by roasting 950 g of As2S3?

3.      Sulfur dioxide is formed during the combustion of carbon disulfide according to the following
        unbalanced reaction:
                          ___CS2 + ___O2  ___CO2 + ___SO2
        a) What mass of SO2 would be produced from 0.0781 g of CS2?
        b) If the actual yield of SO2 was 0.108 g, what is the percent yield for the reaction?

4.      Phosphorous trichloride is produced from the reaction of white phosphorous, P 4, and chlorine
        gas.
        a) Write a balanced equation for this reaction.
        b) A 15.8 g sample of phosphorous trichloride was collected from the reaction of 5.20 g P 4 with
           excess chlorine. What is the percent yield for the reaction?

5.      Aqueous silver nitrate reacts with aqueous magnesium chloride to form solid silver chloride and
        aqueous magnesium nitrate.
        a) Write a balanced chemical equation for this reaction.
        b) If 0.5611 g of silver nitrate is used to produce 0.431 g of silver chloride, calculate the percent
           yield for the reaction.

6.      In the Haber process, ammonia is produced from the reaction of hydrogen gas with nitrogen gas.
        a) Write a balanced equation for this reaction.
        b) If 29.4 g of nitrogen produces 21.2 g of ammonia, what is the percent yield of the reaction?


7.      Trinitrotoluene (TNT), an explosive, is produced from toluene and nitric acid.
                 C7H8(l) + HNO3(aq)  C7H5N3O6(l) + H2O(l)

        a) How many grams of nitric acid are required to react with 307 grams of C7H8?
        b) How many grams of TNT can be produced from 568 grams of C7H8 when an excess of nitric
           acid is used?
        c) What is the percent yield in (b) if 1025 grams of TNT are actually produced?
Chem. 1010 Tutorials                                                                                              Winter 2009

8.      Gallium oxide solid is formed when gallium metal reacts with oxygen at high temperatures. The
        balanced chemical equation representing this reaction is:
                        4 Ga(s) + 3 O2 (g)           2 Ga2O3(s)
        How many grams of Ga2O3(s) can be produced from 9.75 g of Ga(s)?

9.      When the following equation is not balanced, how many moles of CaCl2(s) are needed to
        produce 10.0 g of KCl?
                     CaCl2(s) +          K2CO3(aq)            KCl(aq) +          CaCO3(s)

                      a) 14.9 mol           b) 0.268 mol           c) 0.0671 mol     d) 0.0753 mol     e) 0.134 mol

10.     What is the maximum number of moles of water that can be produced from the combustion of
        28.46 g of C10H22?
                a) 1.1        b) 1.4         c) 1.8           d) 2.0         e) 2.2




Answers:

1.
          CH3OH                                       O2                                  CO2                         H2O
      (grams reacted)                           (grams reacted)                     (grams produced)            (grams produced)

             32.0 g                                  47.9 g                              44.0 g                       36.0 g

             42.7 g                                  64.0 g                              58.7 g                       48.0 g

             16.0 g                                  24.0 g                              22.0 g                       18.0 g

             32.0 g                                  48.0 g                              44.0 g                       36.0 g


2.      742 g of SO2

3.      a) 0.131 g SO2
        b) 82.2 % yield

4.      a) P4 +       6 Cl2                4 PCl3

        b) 68.5 % yield

5.      a)    2 AgNO3(aq) +           MgCl2(aq)       2 AgCl(s)     +    Mg(NO3)2(aq)

        b) 91.0 % yield

6.      a) 3 H2 (g)     + N2(g)                       2 NH3(g)

        b) 59.3 % yield

7.      a) 6.30 x 102 g HNO3

        b) 1.40 x 103 g C7H5N3O6

        c) 73.2 % yield

8.      13.1 g of Ga2O3

9.      c)    CaCl2(s)            +   K2CO3(aq)                   2 KCl(aq) +       CaCO3(s)

10.     e

				
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