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Kw, Ka and Kb

I'm trying to distinguish between Kw, Ka and Kb and their relationship with one another if any?
My teacher has basically said that Ka and Kb are the same thing but i dont understand how. and also how does Kw link in with any of this?

Reply 1

cilla_e

Original post by Gingerbread Girl

Ka is the acid dissociation of weak acids.
Consider the reaction CH3COOH==> CH3COO- + H+
The acid dissociation would be Ka= [H+]x[CH3COO-] / [CH3COOH]

Kb is the base dissociation of weak base
The base dissociation would be similar to that of acids(Except with base in the equation)

Kw is the ionic product of water
Consider the dissociation of water [H2O]==> [H+]x[OH-]
Kw= [H+][OH-]

The H2O "Cancels out" because its value of too big and it becomes incorporated into the value of Kw.

This can be used to prove that a solution is neutral because:
For a neutral solution Kw= [H+][OH-]

I hope that this helps! if you have any more questions feel free to PM me. chemistry can get be quite tricky at times

From a Fellow A-level chemistry student

Reply 2

Rather_Cynical

K_a and K_b pretty much is the same thing, except you're looking for different molecules (for bases, it's the OH^- _(aq)that you're concerned about instead of H⁺ _(aq)in acid) because OH^-_(aq) is a strong proton acceptor. K_w is exactly as cilla_e has already described.