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PPM conversion

  1. Oct 30, 2013 #1
    1. The problem statement, all variables and given/known data

    A 185 m3 room must be filled with 4 ppm NO2 gas (Nitrogen dioxide). The gas comes in cylinder of 200 bar and 50 liters (20x50 = 10,000 liters) and 50 ppm. How many cylinders are needed?

    2. Relevant equations

    1 ppm = 1/1,000,000 (parts per million)
    (can't think of more relevant equations)

    3. The attempt at a solution

    To be honest I do not know how to begin. The ppm part is completely new to me.
     
    Last edited by a moderator: Oct 30, 2013
  2. jcsd
  3. Oct 30, 2013 #2

    Borek

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    If ppm is 1/1,000,000, what mass of the NO2 is needed for 1 ppm if there are 1,000,000 kg of the air?
     
  4. Oct 30, 2013 #3
    Molar mass of NO2 is 46 g/mol.

    Does that mean we need 1/1,000,000th of the above?
     
  5. Oct 30, 2013 #4

    Borek

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    Molar mass doesn't matter for now. Try to answer my question.

    Note: question is incomplete, as it doesn't state if it is v/v or w/w ppm, these are two different cases (which will give slightly different answers).
     
  6. Oct 30, 2013 #5
    What do you mean by v/v or w/w ppm?

    Sorry, your question is not clear enough.
     
  7. Oct 30, 2013 #6

    Borek

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    v/v - volume by volume (as in 1 L in 1,000,000 L)

    w/w - weight by weight (as in 1 kg in 1,000,000 kg).

    I am afraid my question is extremely basic and quite clear, if you have problems answering it you will have problems solving the original questions.

    Let's try from the other end - if there are 10 kg of substance in 1,000,000 kg of the air, what is its ppm concentration?
     
  8. Oct 30, 2013 #7
    That is 10/1,000,000 = 0.00001 or 10 ppm

    Btw the original question is in v/v.
     
  9. Oct 30, 2013 #8

    Borek

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    OK, v/v means it will be easier to solve.

    10 L in 1,000,000 L is 10 ppm.

    What gas volume is present in 1,000,000 L of air if the concentration is 1 ppm?
     
  10. Oct 30, 2013 #9
    For gases, ppm usually refers to mole fraction x 106. What I can't figure out is how the mole fraction can increase from 4 ppm to 50 ppm, unless some reaction is occurring. Is there an equilibrium reaction involved?
     
  11. Oct 31, 2013 #10
    That is 1 liter.
     
  12. Oct 31, 2013 #11
    No, there is no chemical/equilibrium reaction involved.
     
  13. Oct 31, 2013 #12

    Borek

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    So, can you calculate what volume of NO2 required, knowing the volume of the room?

    I must admit I initially missed then 50 ppm part and I am not sure how to understand it. Perhaps it just means NO2 will be diluted.
     
  14. Nov 4, 2013 #13
    They require a solution of 50 ppm NO2 with some unreactive gas in the cylinder.
     
  15. Nov 4, 2013 #14

    Borek

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    So it is just dilution most likely.

    How many liters of NO2 in 185 m3 at 4 ppm?
     
  16. Nov 4, 2013 #15
    The amount is not given. All the given values are mentioned in the question.

    I know this is quite tricky one.
     
  17. Nov 4, 2013 #16

    Borek

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    There is nothing tricky about the problem.

    You were already able to calculate volume of gas present in 1,000,000 L of air when the concentration is 1 ppm. Volume of NO2 in 185 m3 at 4 ppm is identical kind of a problem, just with different numbers. No magic here, simple application of exactly the same principle.
     
  18. Nov 4, 2013 #17
    Are you trying to imply that since 185 m3 equals to 185,000 liters, the 4 ppm of NO2 amounts to 21.6 liters?
     
  19. Nov 4, 2013 #18

    Borek

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    I am not "trying to imply" anything, I am trying to make you think.

    No idea how you got 21.6 liters, and unfortunately it is not the correct number.
     
  20. Nov 4, 2013 #19
    I understand that you are trying to help me out here and I appreciate it.

    What I don't get is how to change the 185 m3 into ppm and then calculate how much 4 ppm amounts to.
     
  21. Nov 4, 2013 #20

    Borek

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    Sorry, you have lost me. You don't change 185 m3 to ppm, one is volume, the other is concentration, you can't change one into another.

    Let's try again:

    In 1,000,000 liters 1 ppm means 1 L - that's what we already know.

    In 1,000,000 liters 4 ppm means ..... L.

    In 1,000 m3 4 ppm means ..... L.

    In 100 m3 4 ppm means ..... L.

    In 185 m3 4 ppm means ..... L.
     
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