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Homework Help: Chemistry problem

  1. Feb 1, 2013 #1
    The problem statement, all variables and given/known data

    40 cm3 of a gas was exploded with 40 cm3 of oxygen (known to be in excess). Under the conditions used, only hydrogen and carbon monoxide reacted with oxygen. On cooling the mixture to room temperature, the volume was 51 cm3. On adding concentrated KOH, the volume decreased further to 41 cm3 as CO2 was absorbed.

    a. Write equations (including the state symbols at room temperature) for the reactions which occur on explosion.

    b. What are the relative volumes of gaseous reactants to gaseous products in these reactions?

    c. What volume of carbon dioxide is produced?

    d. What is the volume of carbon monoxide in the original 40 cm3 of gas?

    e. What is the total decrease in volume as a result of the explosion?

    f. What decrease in volume is caused by (1) CO and (2) H2 on explosion?

    g. What are the volumes of (1) H2 and (2) N2 in the original 40 cm3 of gas?

    The attempt at a solution

    a. 2 H2 (g) + O2 (g) > 2 H2O (l)
    2 CO (g) + O2 (g) > 2 CO2 (g)
    b. 2 + 1 : 2 = 3 : 2

    I feel like I'm missing something really obvious after that...
  2. jcsd
  3. Feb 2, 2013 #2
    When adding the KOH, 51-41=10 cm^3 CO2 is absorbed. From this you know the amount of CO as well, because each CO2 molecule is produced from one CO.

    The decrease of the volume is due to the liquid H2O (the volume of the liquid can be neglected when compared to the volume of the gas), which comes from H2, so from this you can calculate the amount of H2 in the original gas.

    So you know the volume of CO and H2. Hopefully, their sum is less then 40 cm^3 :)
    The rest must be N2, which does not react with oxygen (in this setup).
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