Turn on thread page Beta
    • Thread Starter
    Offline

    16
    ReputationRep:
    Hi guys,

    Just wondering whether anyone could explain this to me... my textbook says:

    In pure water [H+(aq)] = [OH-(aq)] which I get, it's neither acidic or alkaline

    Kw = 1x10^-14 mol^2dm^-6 which I get because it stated that at 298K Kw = [H+][OH-] so Kw is usually about 1x10^-14 mol^2dm^-6 at 298K

    I then says (and this is the bit I don't understand) Kw = [H+(aq)]^2
    Why is this so and where did it come from?

    Thanks in advance for any help
    Offline

    2
    ReputationRep:
    (Original post by Blake Jones)
    Hi guys,

    Just wondering whether anyone could explain this to me... my textbook says:

    In pure water [H+(aq)] = [OH-(aq)] which I get, it's neither acidic or alkaline

    Kw = 1x10^-14 mol^2dm^-6 which I get because it stated that at 298K Kw = [H+][OH-] so Kw is usually about 1x10^-14 mol^2dm^-6 at 298K

    I then says (and this is the bit I don't understand) Kw = [H+(aq)]^2
    Why is this so and where did it come from?

    Thanks in advance for any help
    In pure water there is one H+ for every OH- ion, so [H+] = [OH-]
    thus: Kw = [H+]^2
    Offline

    18
    ReputationRep:
    (Original post by Blake Jones)
    Hi guys,

    Just wondering whether anyone could explain this to me... my textbook says:

    In pure water [H+(aq)] = [OH-(aq)] which I get, it's neither acidic or alkaline

    Kw = 1x10^-14 mol^2dm^-6 which I get because it stated that at 298K Kw = [H+][OH-] so Kw is usually about 1x10^-14 mol^2dm^-6 at 298K

    I then says (and this is the bit I don't understand) Kw = [H+(aq)]^2
    Why is this so and where did it come from?

    Thanks in advance for any help
    As if [H+] = [OH-]
    And Kw = [H+][OH-]
    Then multiplying by [OH-] would be the same as multiplying by [H+]

    Thus Kw = [H+]2

    Does that make sense now?
    • Thread Starter
    Offline

    16
    ReputationRep:
    (Original post by Qinge)
    In pure water there is one H+ for every OH- ion, so [H+] = [OH-]
    thus: Kw = [H+]^2
    Oh! Because there are 2H atoms effectively so the concentration is double so then it goes to squared as it's a concentration, got it! Thanks mate!
    • Thread Starter
    Offline

    16
    ReputationRep:
    (Original post by KaylaB)
    As if [H+] = [OH-]
    And Kw = [H+][OH-]
    Then multiplying by [OH-] would be the same as multiplying by [H+]

    Thus Kw = [H+]2

    Does that make sense now?
    Yeah I get that now, thank you so much you guys! Don't know why I didn't see that before! XD
    Offline

    18
    ReputationRep:
    (Original post by Blake Jones)
    Yeah I get that now, thank you so much you guys! Don't know why I didn't see that before! XD
    No problem! :hat2:
    Offline

    17
    ReputationRep:
    (Original post by Blake Jones)
    Oh! Because there are 2H atoms effectively so the concentration is double so then it goes to squared as it's a concentration, got it! Thanks mate!
    That makes it look like you didn't get it.

    If you had some water at 298 K, the pH would be 7.00

    [H+] = 10-pH = 10-7.00 = 0.0000007 mol dm-3

    The only way you can make H+ ions from water also makes OH- ions. So the concentration of OH- ions must also = 10-7.00. Both of them have that concentration, neither have double that value.

    Kw = [H+] x [OH-] = 10-7.00 x 10-7.00 = [H+]2
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 5, 2017
Poll
Do you think parents should charge rent?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.