Sometimes
it is necessary to use one solution
to make a specific amount of a more
dilute solution. To do this, you can
use the formula:

V1C1 =
V2C2

where:

V1 = volume of starting
solution needed to make the new solution

C1 = concentration of starting
solution

V2 = final volume of new
solution

C2 = final concentration
of new solution

For example: Make 5mL of a 0.25M solution from 2.5mL of a 1M solution.

V1C1 =
V2C2

(V1)(1M) = (5mL)(0.25M)

V1 = [(5mL)(0.25M)] / (1M)

V1 = 1.25mL

So you will need to use 1.25mL of the 1M solution. Since you want the diluted
solution to have a final volume of 5mL, you will need to add ( V1-V2
= 5mL - 1.25mL) 3.75mL of diluent.