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Reaction of acetic acid (CH3COOH) with potassium hydroxide (KOH)

  1. May 14, 2013 #1
    1. The problem statement, all variables and given/known data

    Balance the following equation and write the corresponding
    ionic and net ionic equation (if appropriate):

    CH[itex]_{3}[/itex]COOH [itex]_{(aq)}[/itex]+ KOH [itex]_{(aq)}[/itex] [itex]\rightarrow[/itex]


    2. Relevant equations

    None as far as I know.

    3. The attempt at a solution

    I wrote:

    CH[itex]_{3}[/itex]COOH [itex]_{(aq)}[/itex]+ KOH [itex]_{(aq)}[/itex] [itex]\rightarrow[/itex] CH[itex]_{3}[/itex]COOK [itex]_{(aq)}[/itex] + H[itex]_{2}[/itex]O [itex]_{(l)}[/itex]

    But this is the wrong answer.

    I don't understand why K[itex]^{+}[/itex] does not form a compound with CH[itex]_{3}[/itex]COO[itex]^{-}[/itex]. Can anyone tell what concept or law/theorem controls what compounds form and what compounds do not form? Why is K[itex]^{+}[/itex] a spectator ion in this reaction?
     
  2. jcsd
  3. May 14, 2013 #2

    Borek

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    Staff: Mentor

    Your reaction equation is OK, it just doesn't answer the question - you were asked to write ionic and net ionic reactions. Which of the compounds present in the reaction will be fully dissociated?

    Note: format indices in your formulae with [noparse] and [/noparse] tags, not with LaTeX. And state of matter should be normal text, on the same level as the formula (so dissolved potassium acetate is [noparse]CH3COOK(aq)[/noparse] - rendered as CH3COOK(aq)).
     
  4. May 14, 2013 #3
    So my initial line of thinking was:

    Molecular Equation:
    CH3COOH (aq)+ KOH (aq) → CH3COOK (aq) + H2O (l)

    Ionic Equation:

    CH3COO- (aq) + H+ (aq) + K+ (aq) + OH- (aq) → CH3COO- + K+ + H2O (l)

    Net Ionic Equation:

    H+ (aq) + OH- (aq) → H2O (l)

    This is incorrect.

    But I reasoned that CH3COO- is a weak acid so all of the things in the textbook about not dissociating 100% must come into play here.

    Therefore,

    Molecular Equation:
    CH3COOH (aq)+ KOH (aq) → CH3COOK (aq) + H2O (l)

    Ionic Equation:

    CH3COOH (aq) + K+ (aq) + OH- (aq) → CH3COO- +K+ + H2O (l)

    Net Ionic Equation:

    CH3COOH (aq) + OH- (aq) → CH3COO- + H2O (l)

    That is correct according to the answers in the text.

    How come CH3COO- and K+ do not form a compound though? Is there anyway to calculate or know why? Is it because CH3COOH is not dissociated 100% in solution? (it is a weak acid.)

    Thanks for the help with writing the equations.
     
    Last edited: May 14, 2013
  5. May 14, 2013 #4
    In the ionic equation, K+ and CH3COO- are dissociated because CH3COOK is a strong electrolyte. While CH3COOK is a weak acid so it doesn't dissociate 100%.

    Is this correct. I'm surprised the text doesn't explain this. Borek, can you recommend any comprehensive, first year university chemistry textbooks?
     
  6. May 15, 2013 #5

    Borek

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    Staff: Mentor

    Imagine a solution containing equal concentrations of CH3COO-, Cl-, K+ and Na+ - you can't tell what compounds it contains, there is more than one answer. So we don't name these compounds at all, it is safer to simply list ions.

    Sorry, I can't be of much help when it comes to books - unless you are interested in Polish ones :wink: Chang and Pauling are usually praised as good titles.
     
  7. May 15, 2013 #6
    So the explanation that "In the ionic equation, K+ and CH3COO- are dissociated because CH3COOK is a strong electrolyte. While CH3COOH is a weak acid so it doesn't dissociate 100%." is incorrect? Or it doesn't make sense?

    I'm reading Chang right now actually.
     
  8. May 15, 2013 #7
    I meant to say CH3COOH is a weak acid, not CH3COOK. My idea is that CH3COOK is a strong electrolyte so it dissociates 100% in solution therefore leaving K+ and CH3COO- in solution.
     
  9. May 15, 2013 #8

    Borek

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    Staff: Mentor

    This part was OK, I just tried to answer your other question.
     
  10. May 15, 2013 #9
    Oh, ok. I thought the two questions answered the same thing. Anyway I have a better idea of how to tell what products will arise from certain reactants. Thank you for the help.
     
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