pKa and pKb

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Lindsey Chheng 1E
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Joined: Fri Aug 30, 2019 12:16 am

pKa and pKb

Postby Lindsey Chheng 1E » Wed Jan 22, 2020 10:21 am

why does a smaller pKa or pKb correspond to a stronger acid and strong base?

Posts: 117
Joined: Thu Jul 25, 2019 12:16 am

Re: pKa and pKb

Postby WesleyWu_1C » Wed Jan 22, 2020 12:32 pm

A strong acid would have a higher Ka. For example, a strong acid could have Ka = 10^-1. The formula for pKa is pKa = -logKa. If you do -log(10^-1), you get pKa = 1. Therefore this strong acid has a low pKa.

I like to first think about Ka and then work backwards. A higher Ka means 10^-x where x is a small integer like 1, 2, etc. We know that -log(10^-x) is equal to x, which means a stronger acid has a lower pKa.

I hope this helps.

Tai Metzger 3K
Posts: 103
Joined: Sat Aug 24, 2019 12:17 am

Re: pKa and pKb

Postby Tai Metzger 3K » Wed Jan 22, 2020 12:44 pm

the function p has a negative sign, resulting in larger inputs having smaller outputs. Thus, a larger Ka (and stronger acid) would have a smaller pKa.

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