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How many moles of ions are present

  1. May 12, 2008 #1
    I thought this is a pretty easy problem and I can't believe I did it wrong. What did I do wrong?

    How many moles of ions are present in 250mL of 4.4 M solution of sodium sulfate?

    Here what I did:
    250 mL = .25 L
    mol Na2(SO)4 = MV = 4.4 * .25 = 1.1 mol

    but the answer was 3.3 mol
     
  2. jcsd
  3. May 12, 2008 #2
    Because the question asks how many ions are present, you need to multiply the moles of sodium sulfate by the number of ions it breaks down into in water.

    In this case, I believe the Na2(SO)4 will dissociate to make two Na+ ions and one (SO)4 ion (total of 3 ions).
     
  4. May 12, 2008 #3
    Thanks
     
  5. May 12, 2008 #4
    Another one:
    Water can be decomposed by the passage of an electric current according to the equation 2H2O (l) ---> 2H2 (g) + O2 (g)
    How many moles of H2 (g) can be produced from the passage of 4.8*10^21 electrons?

    I solved:
    4.8*10^21 / 6.022*10^23 * 2 = 1.6*10^-2 mol

    What did I do wrong?
     
  6. May 12, 2008 #5

    Borek

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    Staff: Mentor

    How many electrons needed per each H2 molecule?

    Borek
     
    Last edited by a moderator: Aug 13, 2013
  7. May 12, 2008 #6
  8. Apr 10, 2010 #7
    Re: Moles

    yea really I need answer for her question fast :S I have OLYMPIAD Tomorrow. Thanks :smile:
     
  9. Apr 10, 2010 #8

    Borek

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    Re: Moles

    Which question?
     
    Last edited by a moderator: Aug 13, 2013
  10. Apr 10, 2010 #9

    Gokul43201

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    Staff Emeritus
    Science Advisor
    Gold Member

    Re: Moles

    I'm sorry, but this forum does not work that way. Please read the forum rules first.
     
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