# Finding the value of the ionization for an acid

So this is probably going to look like a ridiculously easy question, but I'm stumped. I have searched for hours looking for a formula to use, and I've given up on my text.

Question: A 0.1 mol/L aqueous solution of weak monoprotic acid has a hydrogen ion concentration of 0.001 mol/L. The value of the ionization, Ka, for this acid is:
a) 10^-6
b) 10^-2
c) 10^-3
d) 10^-5

Now I want to use the formula Ka=[H+] [A-] / [HA] whcih would give me
Ka= [0.001] [A-] / [0.1]. The answer makes no sense. I have no idea where to go next. Can anyone point me in the right direction???

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GCT
Homework Helper
The Ka represents concentrations at equilibrium. the original concentration of the acid is .100mol/L, find the equilibrium concentration. Assume that .001 mol/L of acid has dissociated.

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Gokul43201
Staff Emeritus