The dilution law, expressed by the formula
, states that the moles of solute remain constant when solvent is added to a solution, meaning the product of molarity (
) and volume (
) before dilution equals the product after dilution. This allows for calculating the volume needed to dilute a high-concentration (stock) solution to a desired lower concentration.
Key Concepts and Formula
Formula:
: Initial molarity (concentration) of the stock solution

: Initial volume of the stock solution

: Final molarity of the diluted solution

: Final volume of the diluted solution
Key Takeaways
Constant Solute: Dilution only adds solvent, not solute; thus, moles of solute (
) are identical before and after.
Units: While molarity is

, the volume units (


) only need to be consistent (e.g., both mL or both L).
Preparation: Used in laboratories to make lower-concentration solutions from a high-concentration stock.
Example Calculation
If you have
of a
solution (
) and dilute it to

(
), the new concentration (
) is:



Important: Dilution always results in a lower molarity and higher volume.