One of my past exam papers asks the following:
A fraction of dissociated molecules of a weak monoprotic acid in its 0.09 mol/dm3 aqueous solution is only 10%. What is the Ka?
I used the formula Ka = [H+][A-]/[HA], plotted in and got the answer:
(0.09*0.1)(0.09*0.1)/(0.09) = 9x10-4
But the answer section says Ka = 10-3
Is my calculation wrong?