pKa and Ka

Acidity
Basicity
The Conjugate Seesaw

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Jedrick Zablan 3L
Posts: 68
Joined: Sat Aug 17, 2019 12:17 am

pKa and Ka

Postby Jedrick Zablan 3L » Fri Dec 06, 2019 2:27 am

Hello! What exactly are pKa and Ka and what are they used? Thanks.

Jessica Booth 2F
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

Re: pKa and Ka

Postby Jessica Booth 2F » Fri Dec 06, 2019 10:55 am

Ka is the acid dissociation constant and is equal to [H+][A-]/[HA]. The pKa is the -log of the Ka. The Ka and pKa tell you the strength of a weak acid. The larger the Ka and the smaller the pKa the stronger the acid.

SGonzales_3L
Posts: 55
Joined: Thu Jul 11, 2019 12:17 am

Re: pKa and Ka

Postby SGonzales_3L » Fri Dec 06, 2019 11:09 am

One thing to know that Dr. Lavelle mentioned in class is that if a pKa value is given it is highly likely that that acid is a weak acid. Strong acids strongly favor the products and, thus, have an astronomically large Ka.
Last edited by SGonzales_3L on Fri Dec 06, 2019 5:55 pm, edited 2 times in total.

Joseph Saba
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Joined: Thu Jul 11, 2019 12:16 am

Re: pKa and Ka

Postby Joseph Saba » Fri Dec 06, 2019 11:10 am

SGonzales_3L wrote:One thing to know that Dr. Lavelle mentioned in class is that if a pKa value is given it is highly likely that that acid is a weak acid. Strong acids strongly favor the products and, thus, have an astronomically large pKa.

Does that mean strong acids have a high conc of H+?

SGonzales_3L
Posts: 55
Joined: Thu Jul 11, 2019 12:17 am

Re: pKa and Ka

Postby SGonzales_3L » Fri Dec 06, 2019 11:19 am

Joseph Saba wrote:
SGonzales_3L wrote:One thing to know that Dr. Lavelle mentioned in class is that if a pKa value is given it is highly likely that that acid is a weak acid. Strong acids strongly favor the products and, thus, have an astronomically large pKa.

Does that mean strong acids have a high conc of H+?


Yes, strong acids dissociate almost completely. So in comparison to the concentration of the acid itself, e.g. HA, there would be a higher concentration of H+ ions in aqueous solution. Thus, the Ka is large and the pKa is small.
Last edited by SGonzales_3L on Fri Dec 06, 2019 5:54 pm, edited 3 times in total.

Sartaj Bal 1J
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Joined: Thu Jul 25, 2019 12:17 am

Re: pKa and Ka

Postby Sartaj Bal 1J » Fri Dec 06, 2019 11:26 am

In response to the previous post, I believe a lower pKa and larger Ka are actually representative of a strong acid. A higher Ka value is indicative of a larger concentration of hydronium (H3O+) ions.

Astrid Lunde 1I
Posts: 103
Joined: Sat Sep 07, 2019 12:16 am

Re: pKa and Ka

Postby Astrid Lunde 1I » Fri Dec 06, 2019 11:41 am

Joseph Saba wrote:
SGonzales_3L wrote:One thing to know that Dr. Lavelle mentioned in class is that if a pKa value is given it is highly likely that that acid is a weak acid. Strong acids strongly favor the products and, thus, have an astronomically large pKa.

Does that mean strong acids have a high conc of H+?


Yes, the pKa is so large that we do not calculate it. So we know when we are asked to calculate a pKa value it is a weak acid.

SGonzales_3L
Posts: 55
Joined: Thu Jul 11, 2019 12:17 am

Re: pKa and Ka

Postby SGonzales_3L » Fri Dec 06, 2019 5:56 pm

Sartaj Bal 3H wrote:In response to the previous post, I believe a lower pKa and larger Ka are actually representative of a strong acid. A higher Ka value is indicative of a larger concentration of hydronium (H3O+) ions.


Oops, yes that is my bad. I've edited my comments so they should be correct now. But yes, a stronger acid has higher Ka and thus, smaller pKa.

Bryce Barbee
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Joined: Wed Sep 18, 2019 12:20 am

Re: pKa and Ka

Postby Bryce Barbee » Fri Dec 06, 2019 7:02 pm

Ka is the concentration of products over reactants and pka is the -log of that.

philipraj_1F
Posts: 52
Joined: Fri Aug 30, 2019 12:16 am

Re: pKa and Ka

Postby philipraj_1F » Sun Dec 08, 2019 6:22 pm

When pKa increases, Ka decreases. They are used for weak acids mostly


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