In the histology laboratory, concentrated solutions can be diluted to prepare less concentrated solutions. For example, working solutions of a particular chemical may be prepared from an existing stock or a stronger solution of that chemical very easily.
The following formula, derived from the ratio and proportion formula, will allow changes in concentrations between two solutions:
C1 × V1 = C2 × V2
where
- C1 = stock concentration (beginning concentration)
- V1 = volume of stock required to prepare new solution
- C2= concentration of new or working solution (desired concentration)
- V2= volume of new solution desired
If you know 3 of the 4 values (and the units are the same on both sides of the equation), the fourth can be calculated.
Example:
A histology student performing a Prussian blue stain for ferric iron needs a 2% potassium ferrocyanide solution to complete the process but only finds a 5% stock solution on the stock room shelf. How many milliliters of the stock will he need to prepare 400 mL of 2% potassium ferrocyanide solution?
2% × 400 mL = 5% × (X) mL
2 × 400 = 5(X)
800 / 5 = X
X = 160 mL of 5% stock solution diluted to 400 mL
