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Collecting gas over water with a eudiometer

  1. Oct 15, 2016 #1
    1. The problem statement, all variables and given/known data
    When, using a eudiometer in a lab to collect gas over water, if you have to switch eudiometers is the final volume of water displaced equal to the water displaced in the first tube + the water displaced in the second, and would the pressure be calculated through the total height displaced?

    i.e.

    Collecting butene gas from a reaction of BuBr and KOH in a 50mL eudiometer tube. The first tube all of the 50mL of H2O is displaced and the second tube 23mL is displaced.
    2. Relevant equations
    Total Volume = Volume displaced in first tube + Volume displaced in second
    Pressure = Pressure of both heights combined

    3. The attempt at a solution
    Total Volume of gas produced = 50mL + 23mL=73mL of gas produced
    Pressure = 50cm+(50-23cm)=770mmH2O
     
  2. jcsd
  3. Oct 15, 2016 #2

    Borek

    User Avatar

    Staff: Mentor

    And what is the alternative?
     
  4. Oct 15, 2016 #3
    just the final volume of water displaced in the second eudiometer tube
     
  5. Oct 15, 2016 #4

    Borek

    User Avatar

    Staff: Mentor

    So, what its the reasoning behind ignoring the first portion of gas collected?

    Imagine using twice larger tube - should you get the same result, or a different one from the same experiment? Would you get the same result if you ignore the volume collected in the first tube?
     
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