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Neutralization reactions

  1. Jul 16, 2014 #1
    (Question) Complete and balance each of the following molecular equations (in aqueous solution); include phase labels. Then, for each, write the net ionic equation.

    (A) NH3 + HNO3 ->

    (Attempt) I thought that the acid HNO3 would just give it's hydrogen to NH3 and make the resulting reaction NH3 + HNO3 -> HNH3 + NO3. However the correct answer is NH3 + HNO3 -> NH4NO3.
     
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  3. Jul 17, 2014 #2

    epenguin

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    Your answer appears to me an answer to the second question on the right lines except you seem to have forgotten they asked for the net ionic equation. So if you answer that more carefully that's what what actually happens, is, then this ionic mixture is called ammonium nitrate formally written with the the book answer. I.e you have to represent it as what they thought it was maybe 150 years ago.

    It's understanding not so much chemistry as what the questioners want and if you can't grasp this IMHO lose an odd point and live with it. :biggrin:
     
  4. Jul 17, 2014 #3

    I answered the first part which was to complete the molecular formula. I don't get your explanation.
     
  5. Jul 17, 2014 #4

    symbolipoint

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    Ammonium nitrate is very soluble. You would expect to be able to represent the reaction:


    NH3+HNO3 ---------->HNH+4 + NO-3
     
    Last edited: Jul 17, 2014
  6. Jul 18, 2014 #5

    epenguin

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    You were asked for an ionic equation but there are no ions in your equation. Symbolipoint has give an ionic equation but there is a typo.
    It could hardly be simpler - between your two starting molecules a proton, H+ , is transferred.

    In solution these ions are all there is. Even when it crystallizes the crystal is a lattice of these ions. It is called ammonium nitrate, think of what any other salt is called, and given the formula in your book. Which is what you will see on a bottle of the crystals like you will see common salt written NaCl and not Na+Cl- which is really what it is.

    And then NaCl and NH4NO3 do represent the composition of the salts.

    I just remembered the way related salts are described sometimes. Related to ammonia are amines and amino acids. In these one or more H of NH3 are substituted by organic groups. And you will easily see bottles labelled "glycine hyrdrochoride HOOCH2NH3.HCl" or the common buffer salt tris(hydroxymethyl)aminomethane) hydrochloride (HOCH2)3CNH2.HCl. Though I can't remember ever having seen straight ammonium salts described that way.

    But this is no big problem, I'm sure you're ready now to re-read your textbook. :biggrin:
     
    Last edited: Jul 18, 2014
  7. Jul 19, 2014 #6

    symbolipoint

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    epenguin is right. I made a typographic mistake.

    This, one digit different, is what should have been:


    NH3 + HNO3 ---------> HNH3+ + NO3-
     
  8. Jul 29, 2014 #7
    I know that this question asks for the ionic formula but my book actually wants you to find the molecular formula and then find the ionic formula. My problem is I don't understand how to do that with neutralization reactions. The books explanation on how to do this is terrible.
     
  9. Jul 29, 2014 #8

    Borek

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    In terms of a simple Arrhenius theory of acids and bases neutralization reaction is

    BOH + HA -> AB + H2O

    (where BOH is a base and HA is an acid).

    What to do with ammonia depends on whether you are taught only Arrhenius theory, or Bronwsted-Lowry theory as well.
     
  10. Jul 29, 2014 #9
    What does that have to do with this (A) NH3 + HNO3 -> ?
     
  11. Jul 29, 2014 #10

    Borek

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    Have you read the very last phrase of my post?

    Which theory have you been taught?
     
  12. Jul 29, 2014 #11
    I have been teaching myself through a book and it mentions both theories.
     
  13. Jul 29, 2014 #12

    Borek

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    So it will be better to apply Bronsted-Lowry to ammonia, which is a proton acceptor (BL base):

    NH3 + H+ -> NH4+

    That's net ionic for the ammonia. NO3- is just a spectator (as nitric acid is considered to be strong and always fully dissociated).
     
  14. Jul 29, 2014 #13
    OK I understand how to get the ionic formula but how do I get the literal formula with the spectators included. So how do I find the formula before I convert it to the ionic formula? The question in the book only included one side of the equation (A) NH3 + HNO3 -> and left the other side blank. How do I first find whats on the other side?
     
  15. Jul 29, 2014 #14

    Borek

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    Many ways of skinning that cat.

    For example: acids react with bases producing salts. What is the acid here, what is the base here, what is the salt that combines them?

    Another approach is to go net ionic first, molecular later. HNO3 is 100% dissociated. What do you have in the solution? What reaction do you expect? What ions will be present in the solution? How can you combine them to produce a salt?
     
  16. Jul 29, 2014 #15
    OK then how do I do start this problem (a) the reaction of solid aluminum hydroxide with nitric acid. So I wrote that out in equation form and got AlOH + HNO3 -> and I figured that you would produce AlNO3 + H2O. Turns out the correct answer is Al(NO3)3 + 3H2O. Where did the extra subscript 3 come in?
     
  17. Jul 29, 2014 #16
    Aluminum will react with water to form a hydroxide. However it will react with water in a way in which the net charge is 0. Being on group 13, you know that aluminum will form an ion with a 3+ charge. Hydroxide on the other hand, is an ion with a -1 charge. In order to find the ratio in which the two ions combine, you must find the least common denominator, being 3, and dividing 3 by the two charges to find the respective ratios. So you will end up with Al1(OH)3.
     
  18. Jul 29, 2014 #17
    Yeah I just realized that. OK so I think that I have gotten the first step now I am having trouble with the ionic equation. So the equation is 2HCN + Ca(OH)2 -> Ca(CN)2 + 2H2O. So I separated all all the ions except water and canceled out the rest. So I got H+ + OH- -> H2O. The correct answer is HCN + OH- -> H2O +CN-
     
  19. Jul 30, 2014 #18

    Borek

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    Quite good - that's the essence of most of the neutralization reactions. However, it requires acid and base to be strong enough to be already dissociated. HCN is a very weak acid, and is dissociated in very small degree, so the solution is dominated by the HCN molecules, hence

     
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