Verified answer

Relationships that you will need:

75ml=75 x 10^-3L

50ml=50 x 10^-3L

Moles=Molarity*Volume(L)

Molarity*Volume(L)=0.200 M NaOH*50 x 10^-3L=0.01 moles of NaOH

Molarity*Volume(L)=0.100 M NaOH*75 x 10^-3L=0.0075 moles of NaOH

Total moles of NaOH=0.01+ 0.0075 = 0.0175 moles of NaOH

Total volume=75 x 10^-3L +50 x 10^-3L=125 x 10^-3 L

[OH–]= M of NaOH= total moles/total volume (L)

[OH–]=0.0175 moles/125 x 10^-3 L=0.14M

[OH–]=0.140 M

*****Answer must contain 3 significant figures

M1V1 + M2V2 = M3V3

(0.200 mol/L) (50.0 mL) + (0.100 mol/L) (75.0 mL) = (x) (125 mL)

x = 0.140 M