Question

Suppose 180 ml of 3.52x10^-4 M NaOH is mixed with 220 mL of 2.47x10^-4 M MgCl2.

a) Find the initial concentrations of OH- (aq) and Mg^2+ assuming the volumes are additive

Answer 1

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-