Ka vs Kb

[Isabelle Hales 1J]

Going off of Dr. Lavelle's example in the review lecture this week, how do you determine whether the reaction you are observing has a Ka or Kb value?

[Alex Mele 2A]

Ka is for acid dissociation, and Kb is for base dissociation.

[Geethika Janga 1L]

Ka is the value used during acid dissociation reactions and Kb is used for bases.

[Christine Ma 3L]

You can just look at the species that is disassociating! If the species that is disassociating is an acid like in the example (ie. produces hydronium ions), then it has a Ka value (which can be calculated using its conjugate base's Kb value). Likewise, if the species that is disassociating is a base (ie. produces hydroxide ions), then it has a Kb value (that can be calculated using its conjugate acid's Ka value). Hope this helps!

[Taylor K 2D]

Usually Ka is associated with acids and Kb with bases. If you need to convert between the two, just use the equation Ka x Kb = Kw = 1x10^-14

[Manseej Khatri 2B]

Adding on, I believe if the equilibrium expression written has [H3O+] or [H+] in the numerator, its a ka expression since its generating H+ in solution, and if it has an [OH-] its a kb expression since its generating OH- in solution.