When in water, MgCl2 dissociates into magnesium ions and Cl- ions and NaOH into Na and OH ions. The equation is as follows:
MgCl2 = Mg2+ + 2Cl-
NaOH = Na+ + OH-
The initial concentrations are as follows:
[Mg2+] = .220( 2.47x10^-4) / .220+.180 = 1.36x10^-4 M Mg2+
[OH-] = .180 (3.52x10^-4) / .220+.180 = 1.58x10^-4 M OH-