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Chemistry: Formula units/ions

  1. Oct 7, 2012 #1
    1. The problem statement, all variables and given/known data

    How many ions are present in 1 formula unit of HI(aq)?
    HBr(g)?
    N2S5?



    2. Relevant equations

    These two questions have the same concept, I believe.
    I went the simple way and thought the answer was 2 for both of them, but apparently that was wrong. Can someone show me how to do this, please?

    3. The attempt at a solution

    Does it have something to do with these compounds being consisted of diatomic molecules?
    HI(aq) is 2, but HBr(g) is not 2. I'm guessing it has something to do with the fact that one is aq and the other is a gas, but how does that affect it? How many ions would HBr(g) have?
    And the N2S5 one is not 7 ions. Why? I am confused. Please help!
     
    Last edited: Oct 7, 2012
  2. jcsd
  3. Oct 7, 2012 #2

    Borek

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    Staff: Mentor

    HI(aq) - where do the ions come from?
     
  4. Oct 7, 2012 #3
    H+ and I- so the answer to that one is 2 ions, right?
    But what I'm confused on is HBr(g). Why wouldn't that also be 2 ions?
     
  5. Oct 7, 2012 #4

    Borek

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    Staff: Mentor

    What is the process that creates H+ and I- in HI(aq)?
     
  6. Oct 7, 2012 #5
    dissociation in aq solution.
    but how does that help me see the HBr? its a gas so it's not dissociating right?
     
    Last edited: Oct 7, 2012
  7. Oct 7, 2012 #6

    Borek

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    Yes.

    Can't help you with the N2S5. As far as I know such compound doesn't exist.
     
  8. Oct 7, 2012 #7
    so i still dont understand HBr would have only 1 ion then? or none?
     
  9. Oct 7, 2012 #8

    Borek

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    Staff: Mentor

    None, it doesn't dissociate, so there are only molecules present.
     
  10. Oct 7, 2012 #9
    ohhh i understand. thank you
    so i know you said that you didnt know about the n2s5.. but since it also doesnt dissociate, it it also 0 ions? does that make sense or no?
    or would it be 2 ions for the n2 and s8? i dont really know, actually.
     
  11. Oct 7, 2012 #10

    Borek

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    Staff: Mentor

    If you HAVE to give some answer other than "question doesn't make sense", then 0 makes the most sense.
     
  12. Oct 7, 2012 #11
    does it have something to do with it being a binary molecular compound?
     
    Last edited: Oct 7, 2012
  13. Oct 7, 2012 #12

    Borek

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    Staff: Mentor

    Sorry, no idea what you are asking about. What does have something to do with N2S5 being a binary molecular compound?

    (actually - in the context of the question - it doesn't matter if it is a binary compound or not, it doesn't exist and the story ends there)
     
  14. Oct 7, 2012 #13
    ok i will talk to my professor about it. thank you so much for your help. i appreciate it.
     
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