[H30+]=[OH-] ???

Moderators: Chem_Mod, Chem_Admin

Megan Verschuur 1C
Posts: 43
Joined: Wed Nov 18, 2020 12:26 am

[H30+]=[OH-] ???

Postby Megan Verschuur 1C » Wed Jan 13, 2021 1:26 pm

In textbook problem 6A.21 which reads:
The value of Kw for water at body temperature (37 degrees Celcius) is 2.1 * 10^-14.
(a) What is the molar concentration of H30+?
(b) What is the molar concentration of OH-?

The answer for both is 1.4 * 10 ^ -7. How do you get this? Do you square root the Kw value? Also, why are they both the same?

Jay Solanki 3A
Posts: 122
Joined: Wed Sep 30, 2020 9:59 pm
Been upvoted: 1 time

Re: [H30+]=[OH-] ???

Postby Jay Solanki 3A » Wed Jan 13, 2021 1:29 pm

Yes you have to square root the Kw value. This is because the water equilibrium involved a one-to-one ratio of hydronium to hydroxide ions, so the equilibrium will result in their equilibrium concentrations being the same. Note that they are only the same in distilled water, since there are no other acids or bases to drastically change the pH. Hope this helps!

Anirudh Mahadev 1G
Posts: 141
Joined: Wed Sep 30, 2020 9:39 pm

Re: [H30+]=[OH-] ???

Postby Anirudh Mahadev 1G » Wed Jan 13, 2021 1:30 pm

Yes that is correct, you would square root the value. This makes sense because water should have a neutral pH of 7, which would happen as a result of hydroxide and hydronium concentrations being equal.

OwenSumter_2F
Posts: 92
Joined: Wed Sep 30, 2020 9:57 pm
Been upvoted: 2 times

Re: [H30+]=[OH-] ???

Postby OwenSumter_2F » Wed Jan 13, 2021 1:50 pm

In addition, anything with both H3O+ and OH- will multiply to the KW, just normally not the same number

OwenSumter_2F
Posts: 92
Joined: Wed Sep 30, 2020 9:57 pm
Been upvoted: 2 times

Re: [H30+]=[OH-] ???

Postby OwenSumter_2F » Wed Jan 13, 2021 1:50 pm

In addition, anything with both H3O+ and OH- will multiply to the KW, just normally not the same number

Justin Lin 1B
Posts: 95
Joined: Wed Sep 30, 2020 9:50 pm

Re: [H30+]=[OH-] ???

Postby Justin Lin 1B » Wed Jan 13, 2021 2:37 pm

Yes you would square root the Kw value because water is neutral, so we know that [H3O+] and [OH-] have to be the same value.

austin-3b
Posts: 62
Joined: Wed Nov 11, 2020 12:18 am

Re: [H30+]=[OH-] ???

Postby austin-3b » Wed Jan 13, 2021 7:49 pm

Since it's neutral, you can assume these concentrations are equal. Therefore, you can assign the same variable (x). You do that, square root every side and you get 1 * 10^-7.

Olivia Smith 2E
Posts: 87
Joined: Wed Sep 30, 2020 9:43 pm

Re: [H30+]=[OH-] ???

Postby Olivia Smith 2E » Wed Jan 13, 2021 9:09 pm

It is only in neutral water too! That this applies. Any other reaction will not have this

Malakai Espinosa 3E
Posts: 91
Joined: Wed Sep 30, 2020 9:50 pm
Been upvoted: 1 time

Re: [H30+]=[OH-] ???

Postby Malakai Espinosa 3E » Wed Jan 13, 2021 9:11 pm

Because the two concentrations are the same, we can both define the values as x. Thus, Kw would be x^2. In order to find the concentration of either, we need to square root the Kw that is given.


Return to “Equilibrium Constants & Calculating Concentrations”

Who is online

Users browsing this forum: No registered users and 1 guest