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pKa and pKb

Posted: Tue Feb 11, 2020 5:45 pm
by Megan Cao 1I
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?

Re: pKa and pKb

Posted: Tue Feb 11, 2020 5:47 pm
by jisulee1C
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.

Re: pKa and pKb

Posted: Tue Feb 11, 2020 7:07 pm
by Bryan Chen 1H
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

Re: pKa and pKb

Posted: Tue Feb 11, 2020 7:16 pm
by VioletKo3F
The equation is pKa = -log Ka. Due to the math, a larger Ka will mean a smaller pKa.

Re: pKa and pKb

Posted: Tue Feb 11, 2020 7:30 pm
by WGaines_2E
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.