## Ka Kb

205150314
Posts: 106
Joined: Wed Feb 20, 2019 12:16 am

### Ka Kb

Just trying to reassure things before the midterm. When exactly can you tell that you would either need Ka or Kb?

J_CHEN 4I
Posts: 54
Joined: Tue Nov 14, 2017 3:01 am

### Re: Ka Kb

Ka is for acids, so the equation would have [H3O+]. Kb is for bases, so the equation would have [OH-].

Ryan 1K
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Re: Ka Kb

If a weak acid is dissociating in solution, then you use Ka, which is the K value for a reaction in which an acid gives off a proton and adopts its conjugate base form. Kb is the opposite in that it is the K value for a reaction in which a base accepts a proton and becomes its conjugate acid, producing OH- in the process. You can use Ka and Kb depending on the direction of the reaction as well. For example, if a problem gives you the Ka and then asks you to calculate the concentration of OH-, you can calculate the Ka using Kw and use an ICE table to calculate the equilibrium concentrations of OH-.

Julia Holsinger_1A
Posts: 50
Joined: Tue Feb 26, 2019 12:16 am

### Re: Ka Kb

What is the difference between pKa and Ka? same for pKb and Kb.

Jacob Motawakel
Posts: 103
Joined: Wed Sep 18, 2019 12:20 am
Been upvoted: 1 time

### Re: Ka Kb

Ka is the equilibrium constant for a weak acid dissociating
Kb is the equilibrium constant for a weak base dissociating
pKa = -log[Ka]
pKb = -log[Kb]

Jarrett Peyrefitte 2K
Posts: 102
Joined: Sat Aug 24, 2019 12:16 am

### Re: Ka Kb

Ka - Acids
Kb - Bases

VioletKo3F
Posts: 103
Joined: Sat Sep 07, 2019 12:18 am

### Re: Ka Kb

Usually, you would need Ka or Kb when the question gives you a concentration of a weak acid/base and asks for the pH or pOH of the solution.

Vinita Saxena 2I
Posts: 58
Joined: Fri Aug 09, 2019 12:16 am

### Re: Ka Kb

Use Ka or Kb when using ICE tables

Jainam Shah 4I
Posts: 130
Joined: Fri Aug 30, 2019 12:16 am

### Re: Ka Kb

Ka is the disassociation constant for a weak acid and for Kb its for a weak base. You typically use them in ICE tables to find how much an acid or base disassociates. If you are dealing with H+ or H30+ use Ka and for OH- use Kb

Jasmine Vallarta 2L
Posts: 102
Joined: Sat Aug 17, 2019 12:18 am

### Re: Ka Kb

Ka is for acids and Kb is for bases

WGaines_2E
Posts: 47
Joined: Mon Nov 18, 2019 12:18 am

### Re: Ka Kb

Use Ka if you are solving for the concentration of an acid and Kb for a base

Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

### Re: Ka Kb

205150314 wrote:Just trying to reassure things before the midterm. When exactly can you tell that you would either need Ka or Kb?

If you have OH- being formed, you need Kb, if you have H+ or H30+, Ka.
Use Kw to convert between the two.