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During lecture, Lavelle said that K does not change when an acid or base is added and that even though [H3O+] > [OH-] or vice versa, the product of them would still be equal to 1.0 x 10^-14. Why is this? I understand that Kw = 1.0 x 10^-14, but if an acid or base is added to water, wouldn't it not be considered water anymore? Or is he only talking about weak acids and bases?
Adding acids and bases do not affect the K value because the concentration must still multiply to 1.0x10^-14. Kw represents the equilibrium constant of water and although concentration of the acid and base in solution may change water is in large excess that it remains unchanged and unaffected by a shift. I am a bit confused by this as well but that's how I understand it.
I remember Lavelle saying that when one concentration increases, the other concentration decreases (but didn't catch why). So when you multiply the two, they still give you 1.0 x 10^-14. In addition, the concentration affects the intensity of the reaction happening, not the ratio of products over reactants. So when there is a higher concentration of reactants, the reaction will happen more intensely.
The way I understood this was that when an acid is added to water, it just introduces more hydrogen ions that will bond with water to create hydronium ions and bond with hydroxide ions to produce water. This is why the hydronium ion concentration will increase while the hydroxide ion concentration will decrease, thereby maintaining the equilibrium constant of water at the same value. Hope this helps!
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