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Forums
How to calculate the Ka if the pH and concentration is known?

How to calculate the Ka if the pH and concentration is known?

leahbaker_x

Could somebody please explain how to calculate the Ka if the pH and concentration is known using the example below:

pH = 3.40
[HA] = 0.010 dm-3

Reply 1

dakin_bar

pH=-log[H^+] so 10^-pH = [h+]
kA=[H+][A-]/[HA] [H+] = [A-] so kA = [H+]^2/[HA] as [H+]=10^-pH kA=[10^-pH]^2/[HA]
So in this example kA=[10^-3.40]^2/[0.010] which equals 1.58*10^-5

Hope this helps

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