Solutions with small concentrations are often prepared by diluting a more concentrated stock solution. A known volume of the stock solution is transferred to a new container and brought to a new volume. Since the total amount of solute is the same before and after dilution, we know that
Co*Vo=Cd*Vd
where Co is the concentration of the stock solution, Vo is the volume of the stock solution being diluted, Cd is the concentration of the dilute solution, and Vd is the volume of the dilute solution. Again, the type of glassware used to measure Vo and Vd depends on how exact the solution’s concentration must be known.