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pKa and pKb

Posted: Wed Jan 22, 2020 10:21 am
by Lindsey Chheng 1E
why does a smaller pKa or pKb correspond to a stronger acid and strong base?

Re: pKa and pKb

Posted: Wed Jan 22, 2020 12:32 pm
by WesleyWu_1C
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.

Re: pKa and pKb

Posted: Wed Jan 22, 2020 12:44 pm
by Tai Metzger 3K
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.