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    Hey all
    I'm just having a problem with the ionic product of water formula.
    I just can't seen to get my head around it!
    So I know it is basically an equilibrium constant, for the equilibrium of water:
    H2O <=> H+ and OH-
    So it should be [H+][OH-]/[H2O]
    (the twos are meant to be small)
    But you are supposed to treat H2O as a constant, and it is hence removed from the equation. Except I don't understand why, it says "there is so little OH- and H+ that the conc of H2O is considered to have a constant value". But then surely this means you are considering OH- and H+ to be 0, which would mean that Kw is 0 too!!

    I am soo confused!! If anyone can help me at all that would be amazing, I've just been going round in circles
    Thanks
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    (Original post by meeee)
    Hey all
    I'm just having a problem with the ionic product of water formula.
    I just can't seen to get my head around it!
    So I know it is basically an equilibrium constant, for the equilibrium of water:
    H2O <=> H+ and OH-
    So it should be [H+][OH-]/[H2O]
    (the twos are meant to be small)
    But you are supposed to treat H2O as a constant, and it is hence removed from the equation. Except I don't understand why, it says "there is so little OH- and H+ that the conc of H2O is considered to have a constant value". But then surely this means you are considering OH- and H+ to be 0, which would mean that Kw is 0 too!!

    I am soo confused!! If anyone can help me at all that would be amazing, I've just been going round in circles
    Thanks
    You are quite right that the equilibrium law gives:

    kc = [H+][OH-]/[H2O]

    But if water is massively in excess and effectively constant then we can define a DIFFERENT constant, kw, that considers only the hydrogen ions and hydroxide ions.

    If you like, think of kw = kc * [H2O]
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    (Original post by charco)
    You are quite right that the equilibrium law gives:

    kc = [H+][OH-]/[H2O]

    But if water is massively in excess and effectively constant then we can define a DIFFERENT constant, kw, that considers only the hydrogen ions and hydroxide ions.

    If you like, think of kw = kc * [H2O]
    omg thankyou soo much! that was just driving me insane!
    Thaaaaanks!
 
 
 
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