## pKa and pKb

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### pKa and pKb

I am a little unsure of how these are calculated and how they share a relationship. Can anyone give me a brief explanation?

Long Luong 2H
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Joined: Thu Sep 19, 2019 12:16 am

### Re: pKa and pKb

PKa is calculated by the -log(kA) and pKb is calculated by the -log(kB). If you add pKa and pKb together, it will equal 14.

Martina
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### Re: pKa and pKb

These are just logarithmic versions of Ka and Kb, their relationship is that they add up to 14.

Mitchell Koss 4G
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### Re: pKa and pKb

always go back to pH= -log[H30+] and pOH= -log[OH-]. From this you can get the other relationships

Christineg1G
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### Re: pKa and pKb

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution and pKb is the negative base-10 logarithm of the base dissociation constant (Kb). pKa and pKb added together equals 14.

saigorijavolu2k
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### Re: pKa and pKb

Think of Pka and Pkb as being calculated pretty much the same exact way as pH, except in this case you could calculate -log(ka) and ka is the acid dissociation constant used for weak acids.

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### Re: pKa and pKb

pka = -log(ka)
pkb=-log(kb)
pka+pkb=pkw
pkw = 14.00 at 25 degrees celsius
ka= 10^-pka
kb=10^-pkb
ka x kb = kw

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### Re: pKa and pKb

pKa and pKb are acidity and basicity constants which are given as their negative log:
pKa=-log(ka)
pKb=-log(kb)

stephaniekim2K
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### Re: pKa and pKb

p just means its the log of something. so pKa is log(Ka) and pKb is log(Kb).

805097738
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### Re: pKa and pKb

pka and pkb are added together to get 14; so, if you know one, you can subtract it from 14 to get the other

Leila_4G
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### Re: pKa and pKb

@stephaniekim2k , That is a really great way of explaining it, thank you! It helped me a lot!

Ayushi2011
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### Re: pKa and pKb

when you are given Ka and Kb, you take -log of that to find pka and pkb. Pka + Pkb = 14

Emil Velasco 1H
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### Re: pKa and pKb

pKa + pKa = Kw (autoprotolysis constant) = 14

This equation can be flipped around respectively to find a value you need.

William Francis 2E
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### Re: pKa and pKb

pKa's are used for acids and pKb's are used for bases. The K value for a reaction between an acid and liquid water is deemed a Ka value. A Kb value is the K value for a reaction between a base and liquid water. pKa's are calculated by taking the negative log of the Ka. pKb's are calculated by taking the negative log of the Kb.

Kylie Lim 4G
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### Re: pKa and pKb

Ka and Kb are calculated the same way as K but for weak acids and bases, with the concentration of products on the top and the concentration of reactants on the bottom. PKa and Pkb are the -log(Ka) and -log(Kb)

Megan Cao 1I
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### Re: pKa and pKb

the sum of pka and pkb is equivalent to the pkw which is 14.
the product of ka and kb is kw, which is 10-14.

ka is the equilibrium constant for an acid.
kb is the equilibrium constant for a base.

it's good to know that the lower the pKa, the higher the Ka, and the stronger the acid; and vice versa. the same also applies to the pKb

kendal mccarthy
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### Re: pKa and pKb

pKa is basically the hydronium concentration while pKb is the hydroxide concentration of a solution. pKa and pKb when added together always equals 14. You can calculate pKa or pKb from having Ka(equilibrium constant for acids) or Kb (equilibrium constant for bases) and taking the negative log.

vanessas0123
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Joined: Wed Sep 11, 2019 12:17 am

pKa = -logKa
pKb = -logKb

pka + pkb = 14