Calculating Ka from pKa

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Mrudula Akkinepally
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Joined: Wed Sep 30, 2020 9:31 pm

Calculating Ka from pKa

Postby Mrudula Akkinepally » Thu Jan 14, 2021 7:49 pm

Hello everyone!

I know that pka is the negative log of ka, but how do we go from pka to ka?

Thank you :)

Liam Bertrand 3
Posts: 82
Joined: Wed Sep 30, 2020 9:53 pm

Re: Calculating Ka from pKa

Postby Liam Bertrand 3 » Thu Jan 14, 2021 7:53 pm

When you have log10(a)=c, to get to exponential form it would be 10^c= a. Thus, since the pka is c in this example, raise 10 to whatever the pka is and it should give you ka. Someone might want to double check me on that one though because its been a while since I've done that kind of math

Emily Vu 1L
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Re: Calculating Ka from pKa

Postby Emily Vu 1L » Thu Jan 14, 2021 8:08 pm

Hi! So the log rules are exactly the same if we were to go from pH to [H3O+], and vice versa. So to convert from pKa to Ka, you take 10-pKa.

Hope this helps!

Tessa House 3A
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Re: Calculating Ka from pKa

Postby Tessa House 3A » Thu Jan 14, 2021 8:56 pm

Because -log(Ka)=pKa, you can rearrange this to get 10^-pKa=Ka. Plug in the pKa and you can get the Ka. You can always just rearrange the original equation to solve for Ka. I hope this helps!

Ziyan Peng 3A
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Joined: Wed Nov 18, 2020 12:29 am

Re: Calculating Ka from pKa

Postby Ziyan Peng 3A » Fri Jan 15, 2021 9:00 am

Ka=10^(-pKa), just like how [H3O+]=10^(-pH) and how [OH-]=10^(-pOH). I find grouping these together easier to remember, especially if you don't want to run the math through your head every time like me :)

Nishka Vipul 1J
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Joined: Thu Dec 17, 2020 12:18 am

Re: Calculating Ka from pKa

Postby Nishka Vipul 1J » Fri Jan 15, 2021 9:38 am

Mrudula Akkinepally wrote:Hello everyone!

I know that pka is the negative log of ka, but how do we go from pka to ka?

Thank you :)


Hi! To calculate Ka from pKa you would use this: Ka=10^(-pKa)! Hope this helps. I would recommend reviewing log rules, it really helped me understand this so that it's not just another equation to memorize.

Stephen Min 1I
Posts: 90
Joined: Wed Sep 30, 2020 10:01 pm

Re: Calculating Ka from pKa

Postby Stephen Min 1I » Fri Jan 15, 2021 1:11 pm

To derive Ka, you would 10^-(pKa). This is because pKa is in the form of -log[Ka]. Its the same format as converting between pH and [H3O+].

Nayra Gharpetian 3F
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Re: Calculating Ka from pKa

Postby Nayra Gharpetian 3F » Fri Jan 15, 2021 2:33 pm

to find Ka from pKa you would do 10^(-pKa)


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