How Ka and Kb relate to each other

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Maayan Epstein 14B
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Joined: Fri Sep 28, 2018 12:20 am

How Ka and Kb relate to each other

Postby Maayan Epstein 14B » Thu Jan 17, 2019 3:32 pm

If Kc of the forward reaction is the inverse of the Kc of the reverse reaction, then does this mean that in an acid-base chemical equilibrium reaction, the conjugate acid would dissociate at the inverse rate that the conjugate base would accept a proton (in the opposite direction)?
If my logic is flawed please explain how!

MaanasO 1A
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

Re: How Ka and Kb relate to each other

Postby MaanasO 1A » Thu Jan 17, 2019 5:10 pm

Hi Maayan!

In the cases of Ka and Kb, we only deal with dissolving the acid or base in question in water. And the Ka and Kb aren't representative of opposite directions of the same reaction. Let's take NH3 (a weak base). The Kb for NH3 deals w/ the reaction that forms NH4+ and OH-. Ka for NH4+ deals w/ the reaction that forms NH3 and H3O+. In other words, we take the weak base and dissolve it in water, we get the Kb. When we put the conjugate acid in, we get the Ka.

Hope that helps!


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