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Spectator Ions and Molarity Questions

  1. Mar 10, 2016 #1

    B3NR4Y

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    1. The problem statement, all variables and given/known data
    An aqueous solution of silver nitrate, AgNO3, reacts with an aqueous solution ammonium carbonate, (NH4)2CO3. What are the spectator ions for the reaction?
    AgNO3 (aq) + (NH4)2CO3 ->

    A 17.5 mL sample of hydrochloric acid HCl solution required 29.6 mL of 0.250M Ba(OH)2 for neutralization. The concentration of hydrocholoric acid was ____ M

    2. Relevant equations
    Molarity = moles/volume

    3. The attempt at a solution
    For the first one I wrote out what I thought the chemical reaction was
    AgNO3 (aq) + (NH4)2CO3 -> AgCO3 + (NH4)2NO3, this is already balanced so separating out the ions would give Ag+ and CO32- as the spectator ions, but this isn't true. The spectator ions are actually NH4+ and NO3- and I have no clue where that comes from.

    For the second all I could think of was finding the moles of Ba(OH)2 by multiplying (0.25) and 29.6 mL, but I don't even know what to do with that number.
     
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  3. Mar 10, 2016 #2

    epenguin

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    Well just as a reminder I hope, you could work out how many moles of OH- that Ba(OH)2 that is, then how many moles of H+ does that react with? (Or if you haven't done ions you can think of it as Ba(OH)2 reacting with HCl to form what salt and what else?)

    Forum homework instructions warn against asking questions saying 'I have no idea...' - the impression is particularly bad when the question is about the very first lesson in some subject. The whole concept of moles comes in from consideration of how much of one thing reacts with another, the very start of chemistry. I have given a hint to but the real beneficial answer should be go back and read about molarity in your textbook.
     
    Last edited: Mar 10, 2016
  4. Mar 10, 2016 #3

    Borek

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    It is not. You got some formulas wrong.

    One of the four substances is marked as (aq), what forms do the other three take?
     
  5. Mar 11, 2016 #4
    NH4 has a positive charge of +1 and NO3 has a negative charge of -1. If you have two ammoniums on one nitrate, then the sum of its charges isn't zero. So it's actually not balanced.
     
  6. Mar 12, 2016 #5

    epenguin

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    Or in other words if you write silver carbonate in the quoted form, valency of carbonate is 2 (or -2 according to what where you've been taught) and silver carbonate is not AgCO3 it's....
     
  7. Mar 14, 2016 #6
    Correct me if I am wrong, but aren't spectator ions those which do not participate in the "reaction"? Like potassium in many reactions of KMnO4? Aren't they a feature of redox reactions where one radical generally gets oxidized/reduced?

    What are spectator ions in a displacement reactions? Do not all radicals participate in the "reaction" here?
     
  8. Mar 14, 2016 #7

    Borek

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    Yes.

    No, they are present in many other reactions as well. And they are quite easy to point to in the reaction posted by OP, once you try to answer question I asked in my previous post.
     
  9. Mar 14, 2016 #8
    The products will be either (aq) or (ppt). How does that help us identify the spectator ions? Are you suggesting this has something to do with H+ and O-H ions?
     
  10. Mar 14, 2016 #9

    Borek

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    What does (aq) mean for a soluble salt? One like NH4NO3?
     
  11. Mar 14, 2016 #10
    It exists as ions. In this case NH4+ and NO3-. It undergoes hydrolysis. Am I going down the right path? OK that explains it. Yeah fine, NO3- and Ag+ should be spectator ions. But the OP differs.
     
  12. Mar 14, 2016 #11

    Borek

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    Dissociation to be precise.

    No. Take a look at all other substances in the reaction equation. One of them is not (aq). Which, why, and what does it mean?
     
  13. Mar 16, 2016 #12
    This should help identify the first question:
    602459221.png
     
  14. Mar 16, 2016 #13
    OK I forgot AgCO3 was a sparingly soluble salt. I knew I was making a silly mistake. Thank you @Eclair_de_XII ..!

    @Borek ... when I said hydrolyse I meant the reaction of CO3-2 with water to give acids. I guess that isn't too relevant here. (Or is it?)
     
  15. Mar 16, 2016 #14

    Borek

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    Wouldn't hurt to keep your formulas correct. We already pointed out some of the formulas from the original post are wrong.

    That's not off, but it is not what dominates the solution. Now that you know silver carbonate is sparingly soluble, can you answer the question from my previous post?
     
  16. Mar 17, 2016 #15
    Goodness gracious. I am sorry. It is Ag2CO3

    OK so Ag2CO3 is sparingly soluble. Thus its ions do not participate in the reaction. As a result, NH4+ and NO3- are the reactant species while the other two are spectators. Am I right?
     
  17. Mar 17, 2016 #16

    Borek

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    They are not present AFTER the reaction, but they are present BEFORE the reaction. What does it tell you about the reaction? Which ions do react?

    Do NH4+ and NO3- change during the reaction?
     
  18. Mar 17, 2016 #17

    epenguin

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    Oh dear, I mean to say, 'spectator'is not some arcane term from Greek or Latin (well not any more), or like2-phenlythanylgondoic ester that you would never meet outside specialised chemistry. It just comes from the English language, which from your profile I expect you are familiar with. I mean know of any sports events? There are the guys who play each other in the match and then there the spectators we don't.

    I hate to see hangups about terminology.. My guess is that some guy one day just wrote in a paper 'spectator ions', maybe in inverted commas (quotes) the first time without the fuss of any formal definition, thinking it was obvious, to refer to these nonparticipating ions. I think it's half possible it has never been pronounced upon by any formal terminology commission.

    I wonder, don't you have any textbook? On as well as the definition, doesn't it give you any examples elsewhere in the book? If not that shows you how important it is anyway. But when I googled I immediately found explanation and examples. And the examples make it surely obvious why they called that
     
  19. Mar 19, 2016 #18
    OK I am unable to figure this out. I don't know what it tells me about the reaction, but I do understand that NH4+ and NO3- react.

    No. They remain as they are and form NH4NO3. Does this mean they are not the reactants? OK I could listen to epenguin and google it up. But I don't like Google. Easy way out. But I would love it if you could explain it.
     
  20. Mar 19, 2016 #19

    Borek

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    That's exactly what I am trying to tell you. They don't change during the reaction, so they are not reactants, they are spectators. Actually they technically don't even form NH4NO3, they are just present as NH4+ and NO3-.

    What other ions were in the solution initially? Are they still left in the solution after the reaction?
     
  21. Mar 22, 2016 #20
    Silver and carbonate were ions before and became part of a precipitate. Now they are not part of the solution. So these are the reactants?
     
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