To solve this we use the equation,
M1V1 = M2V2
where M1 is the concentration of the stock
solution, V1 is the volume of the stock solution, M2 is the concentration of
the new solution and V2 is its volume.
2.5 M x V1 = 0.50 M x .100 L
V1 = 0.02 L or 20 mL
