## pKa and Ka

Acidity $K_{a}$
Basicity $K_{b}$
The Conjugate Seesaw $K_{a}\times K_{b}=K_{w}$

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

### pKa and Ka

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

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

### Re: pKa and Ka

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
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Joined: Thu Jul 11, 2019 12:17 am

### Re: pKa and Ka

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

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

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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### Re: pKa and Ka

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
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Joined: Sat Sep 07, 2019 12:16 am

### Re: pKa and Ka

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

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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### Re: pKa and Ka

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

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

### Re: pKa and Ka

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