C₁V₁ = C₂V₂
The dilution equation C₁V₁ = C₂V₂ is one of the most used formulas in chemistry and biology. It states that the amount of solute remains constant when adding solvent: moles before = moles after. C₁ and V₁ are the initial concentration and volume; C₂ and V₂ are the final values. This equation works for any consistent concentration units (M, mg/L, %, etc.) as long as both sides use the same units. Common applications: preparing lab reagents from stock solutions, diluting buffers for biological assays, pharmaceutical compounding, and environmental water testing. When making dilutions, always add solute to solvent (not the reverse, especially for acids) and mix thoroughly. For very precise work, use volumetric flasks and account for volume changes upon mixing.