How do I dilute 70 % alcohol to 40 %?

Enter C₁ = 70, V₁ = your volume, C₂ = 0 (water) and C_f = 40, and solve for V₂. For 300 mL of 70 %, add 225 mL of water to get 525 mL of about 40 %.

What is the alligation method?

A traditional pharmacy and industry shortcut for mixing two strengths. It gives the same answer as C₁V₁ + C₂V₂ = C_f(V₁ + V₂).

Can the target be outside the two starting concentrations?

No. Mixing can only give a concentration between the two you start with; the calculator reports a negative volume otherwise.

Solution Mixing Calculator | PeriodicElementTable

C₁V₁ + C₂V₂ = C_f × (V₁ + V₂) — fill in every field except the one you want; the empty field is solved for.

Concentration of solution 1 (C₁)Any unit (%, M, g/L) — same for all three

Volume of solution 1 (V₁)

Concentration of solution 2 (C₂)Use 0 for pure water

Volume of solution 2 (V₂)

Final concentration (C_f)

Volume of solution 2 (V₂) = 225 mL

Rearrange: V₂ = V₁ × (C₁ − C_f) ÷ (C_f − C₂)
Substitute: (300 mL) × ((70) − (40)) ÷ ((40) − (0)) = 225 mL

How it works

The calculator applies conservation of solute: C₁V₁ + C₂V₂ = C_f (V₁ + V₂). Concentrations can be in any unit — %, mol/L, g/L — as long as all three use the same one. Volumes are converted to millilitres.

It assumes volumes are additive, which is close for dilute aqueous solutions. Mixing concentrated solutions (for example ethanol and water, or strong acids) changes the total volume slightly, so for exact work measure the final volume or work by mass.

Frequently asked questions

How do I dilute 70 % alcohol to 40 %?: Enter C₁ = 70, V₁ = your volume, C₂ = 0 (water) and C_f = 40, and solve for V₂. For 300 mL of 70 %, add 225 mL of water to get 525 mL of about 40 %.
What is the alligation method?: A traditional pharmacy and industry shortcut for mixing two strengths. It gives the same answer as C₁V₁ + C₂V₂ = C_f(V₁ + V₂).
Can the target be outside the two starting concentrations?: No. Mixing can only give a concentration between the two you start with; the calculator reports a negative volume otherwise.

How it works

Frequently asked questions

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