For a 0.010 M solution of acetic acid in water the hydrogen ion and acetate ion concentrations are both 4.0x10-4 M.

HOAc		H+   +	OAc-
		4.0x10-4 M	4.0x10-4 M

In this solution what is the concentration of unionized acetic acid, HOAc?

4.0x10^-4 M 0.0096 M  0.010 M