A weak acid (HA) is found to ionize 16.2%
when mixed at a concentration of 0.21 mol/L.
What is the value of Ka for this acid?
...............HA ==> H^+ + A^-
initial.......0.21....0.....0
change........-x......x......x
equil...0.21-0.034....0.034..0.034
Where does the 0.034 come from? That's 0.21 x 0.162 = 0.034
Substitute in Ka expression and solve for Ka.