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### Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 10:58 am
If we were given a reaction of a weak acid dissociating, then the reverse reaction would be the conjugate base. So if we are given Ka, can we find Kb by taking the inverse? Or should we use that Ka x Kb = Kw every time?

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 12:14 pm
Just to be safe, I would use what we know. And kA*kb=kw is given so use that.

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 12:23 pm
Since we know KaxKb = Kw that is what should be used to be safe.

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 1:26 pm
If we are not given Ka, can we just find Ka by using an ice table?

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 4:27 pm
lizettelopez1F wrote:If we are not given Ka, can we just find Ka by using an ice table?

I don't think it would be possible to find Ka value using an ice table if we don't know the variable x. We use the ice table so we can calculate the change in concentration knowing the Ka or Kb value. Instead, to find Ka value, you need to know the concentration of all the reactants and products (aqueous and gaseous) so you can set up an equilibrium equation or use the pKa or pKb value.

Hope this help and correct me if I'm wrong. Thanks!

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 7:22 pm
I don't believe I have ever seen Ka and Kb sharing an inverse relationship from the doing the textbook problems. I believe the only relevant relationship is Ka x Kb = Kw.

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 7:32 pm
Using the formula we were given Ka x Kb= Kw will be the best thing to do.

### Re: Ka and Kb as Inverses?

Posted: Sun Jan 20, 2019 7:34 pm
the safest thing to do is use the acid base formula to make sure