Which equation represents the dilution formula used to relate the concentrations and volumes before and after dilution?

• A. C1V1=C2V2
• B. C1V1=C2+V2
• C. C1/V1=C2/V2
• D. V1+C1=V2+C2

Answer: (A)

When you dilute a solution, the amount of solute stays the same. That means the number of moles you start with, C1 times V1, must equal the number of moles in the final solution, C2 times V2. So the relationship is C1V1 = C2V2. This lets you solve for any missing value: if you know the starting concentration and volume and the final volume, you can find the new concentration, or vice versa.

For example, taking 50 mL of a 4 M solution and diluting it to 1 L gives C2 = (4 M × 0.050 L) / 1.000 L = 0.20 M.

The other forms don’t fit dilution physics: they mix different units or misrepresent what’s conserved. For instance, C1V1 = C2 + V2 combines concentration with volume in a non–conservative way, which isn’t dimensionally or conceptually correct. C1/V1 = C2/V2 and V1 + C1 = V2 + C2 similarly don’t reflect the conservation of solute during dilution.