Kw= 1.0 x 10^-14

Moderators: Chem_Mod, Chem_Admin

America Alvarado
Posts: 104
Joined: Sun Oct 04, 2020 12:15 am
Been upvoted: 1 time

Kw= 1.0 x 10^-14

Postby America Alvarado » Mon Jan 11, 2021 7:13 pm

In 1/11 lecture, Lavelle says Kw= 1.0 x 10^-14 therefore H30 and OH must be 1.0 x. 10^-7. How did he come up with 1.0 x 10^-14?

Brittney Nguyen 2L
Posts: 106
Joined: Wed Sep 30, 2020 9:39 pm
Been upvoted: 4 times

Re: Kw= 1.0 x 10^-14

Postby Brittney Nguyen 2L » Mon Jan 11, 2021 7:28 pm

Hi!

This probably isn't too helpful, but I looked around on the internet a lot and it just seems like Kw being equal to 10^-14 is universally accepted. It just... is that. For example, Khan Academy (https://www.khanacademy.org/science/ap- ... ion-and-kw) just straight up says that Kw = 10^-14.

If I had to infer based on things that Dr. Lavelle said during the lecture, I think that Kw is equal to 10^-14 because [H3O+] usually ranges from 1M to 1x10^-14M. Since water is neutral and has equal parts [H3O+] and [OH-], the only values for [H3O+] and [OH-] that work are 1x10^-7. When you plug this value into Kw = [H3O+][OH-], you get Kw = 1x10^-14. Sounds redundant, I know. But I think Kw just has to be 10^-14 because of its autoprotonizing and neutral nature.

Samantha Pedersen 2K
Posts: 121
Joined: Wed Sep 18, 2019 12:21 am
Been upvoted: 9 times

Re: Kw= 1.0 x 10^-14

Postby Samantha Pedersen 2K » Mon Jan 11, 2021 7:31 pm

I believe 1.0 x 10^-14 is an experimentally determined value for water at 25 degrees Celsius that is now a universally accepted value. I hope this helps!

Brian Bui 3H
Posts: 91
Joined: Wed Sep 30, 2020 9:42 pm

Re: Kw= 1.0 x 10^-14

Postby Brian Bui 3H » Mon Jan 11, 2021 8:03 pm

Someone correct me if I'm wrong, but I think it comes from the reaction:

2H2O(l) ---> H3O+(aq) + OH-(aq)

Where the K value is equal to 1.0 x 10-14. Think of it as any other reaction that has its own K value.

When writing K for this reaction, we don't include water because it's a liquid, so it's:

[H3O+] x [OH-] = 10-14

[H3O+] and [OH-] are equal because water is neutral; therefore they must be the same, so they are both 1.0 x 10-7, and (1.0 x 10-7) x (1.0 x 10-7) = 1.0 x 10-14.

Hope this helps!

Devan Nathu - 2H
Posts: 31
Joined: Wed Nov 18, 2020 12:32 am

Re: Kw= 1.0 x 10^-14

Postby Devan Nathu - 2H » Tue Jan 12, 2021 1:50 am

The Kw value at 25C is 1.0 x 10^-14. It is also the designated value for Kw. Because water is neutral, it can be inferred that the [H3O+] and [OH-] concentration will equate to each other and have the same value, which is where 1.0 x. 10^-7 came from.

jessicasilverstein1F
Posts: 122
Joined: Wed Sep 30, 2020 9:57 pm

Re: Kw= 1.0 x 10^-14

Postby jessicasilverstein1F » Tue Jan 12, 2021 2:34 pm

This is just a given value that has been experimentally determined. 1.0 x 10^-14 for water at 25 degrees Celsius.

Norah Gidanian 3D
Posts: 130
Joined: Wed Sep 30, 2020 9:49 pm
Been upvoted: 1 time

Re: Kw= 1.0 x 10^-14

Postby Norah Gidanian 3D » Tue Jan 12, 2021 3:04 pm

I am pretty sure that it is just a constant we are supposed to memorize that was determined experimentally.

Siwa Hwang 3G
Posts: 84
Joined: Wed Sep 30, 2020 9:48 pm

Re: Kw= 1.0 x 10^-14

Postby Siwa Hwang 3G » Tue Jan 12, 2021 5:38 pm

If you multiply the connections of h30 and oh which are both 10^-7, you obtain kw = 10^-14

Nayra Gharpetian 3F
Posts: 86
Joined: Wed Sep 30, 2020 9:40 pm
Been upvoted: 1 time

Re: Kw= 1.0 x 10^-14

Postby Nayra Gharpetian 3F » Tue Jan 12, 2021 5:46 pm

as everyone said above Kw was experimentally determined

America Alvarado
Posts: 104
Joined: Sun Oct 04, 2020 12:15 am
Been upvoted: 1 time

Re: Kw= 1.0 x 10^-14

Postby America Alvarado » Wed Jan 13, 2021 11:52 am

thank you all!

Megan Hulsy 1A
Posts: 114
Joined: Wed Sep 30, 2020 9:51 pm

Re: Kw= 1.0 x 10^-14

Postby Megan Hulsy 1A » Wed Jan 13, 2021 8:02 pm

Hi! This is a constant, so it is naturally known to be 1.0 x 10^-14. :) However, the concentrations of H3O+ and OH- depend and are not always 1.0 x 10^-7 (neutral).

Laura 3l
Posts: 103
Joined: Wed Sep 30, 2020 9:55 pm
Been upvoted: 1 time

Re: Kw= 1.0 x 10^-14

Postby Laura 3l » Wed Jan 13, 2021 8:05 pm

This value is a constant and is given to us because like everyone else has said, it is a value that was experimentally determined.


Return to “Equilibrium Constants & Calculating Concentrations”

Who is online

Users browsing this forum: No registered users and 1 guest