pKa and pKb

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Megan Cao 1I
Posts: 103
Joined: Sat Sep 07, 2019 12:18 am

pKa and pKb

Postby Megan Cao 1I » Tue Feb 11, 2020 5:45 pm

For pKa the greater the value the smaller the Ka value, and the weaker the acid. I understand how the smaller Ka value shows how it's a weak acid, however I can't understand how a greater pKa means a smaller Ka. Could someone possibly explain this?

jisulee1C
Posts: 149
Joined: Thu Jul 25, 2019 12:17 am

Re: pKa and pKb

Postby jisulee1C » Tue Feb 11, 2020 5:47 pm

A greater pKa results in a smaller Ka because pKa = -log Ka. If you plug in values you can see that a stronger acid will have a larger Ka and thus a smaller pKa.

Bryan Chen 1H
Posts: 58
Joined: Mon Jun 17, 2019 7:24 am

Re: pKa and pKb

Postby Bryan Chen 1H » Tue Feb 11, 2020 7:07 pm

it just happens to be this way because of the math. its similar to how a higher pH is less H+ concentration, just like how higher pKa is weaker acid

VioletKo3F
Posts: 103
Joined: Sat Sep 07, 2019 12:18 am

Re: pKa and pKb

Postby VioletKo3F » Tue Feb 11, 2020 7:16 pm

The equation is pKa = -log Ka. Due to the math, a larger Ka will mean a smaller pKa.

WGaines_2E
Posts: 47
Joined: Mon Nov 18, 2019 12:18 am

Re: pKa and pKb

Postby WGaines_2E » Tue Feb 11, 2020 7:30 pm

so mathematically if you say pKa = 1x10^-7, Ka will be 7, and vice versa. To find pKa from Ka you do 10^-(Ka)=10^-7. Say Ka is now 3. Then pKa becomes 1x10^-3. I hope you can see here that a larger Ka leads to a smaller pKa.


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