Ka Kb

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

Ka Kb

Postby 205150314 » Sun Feb 09, 2020 9:34 pm

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

Postby J_CHEN 4I » Sun Feb 09, 2020 9:36 pm

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

Postby Ryan 1K » Sun Feb 09, 2020 9:37 pm

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

Postby Julia Holsinger_1A » Tue Mar 10, 2020 5:54 pm

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

Jacob Motawakel
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Been upvoted: 1 time

Re: Ka Kb

Postby Jacob Motawakel » Tue Mar 10, 2020 6:07 pm

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

Postby Jarrett Peyrefitte 2K » Tue Mar 10, 2020 6:14 pm

Ka - Acids
Kb - Bases

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

Re: Ka Kb

Postby VioletKo3F » Tue Mar 10, 2020 6:41 pm

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

Postby Vinita Saxena 2I » Tue Mar 10, 2020 6:42 pm

Use Ka or Kb when using ICE tables

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

Re: Ka Kb

Postby Jainam Shah 4I » Tue Mar 10, 2020 7:28 pm

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

Postby Jasmine Vallarta 2L » Tue Mar 10, 2020 7:40 pm

Ka is for acids and Kb is for bases

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

Re: Ka Kb

Postby WGaines_2E » Tue Mar 10, 2020 9:27 pm

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

Nicholas_Gladkov_2J
Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

Re: Ka Kb

Postby Nicholas_Gladkov_2J » Tue Mar 10, 2020 9:32 pm

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.


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