We measured the hydrogen ion concentration of 4.0x10^-4 M for a 0.010 M solution of acetic acid.

HOAc		H+   +	OAc-
		4.0x10-4 M

Under these conditions, what is the concentration of acetate ions?

0.010 M  4.0x10^-3 M 4.0x10^-4 M