Acid Dilution Calculator (Add Acid to Water)
Dilute a concentrated acid safely: find how much stock acid and how much water make a target molarity — always adding acid to water.
How it works
C₁V₁ = C₂V₂ → V(acid) = C₂ × V(final) ÷ C₁ · V(water) = V(final) − V(acid)
Dilution conserves moles of acid: the concentration times volume before equals concentration times volume after, so the stock volume you need is simply the target concentration times final volume divided by the stock concentration. The order of mixing is a safety rule, not a maths rule — always add acid to water, never water to acid. Dilution releases heat, and pouring water onto concentrated acid can flash-boil it and spatter, so fill the vessel with most of the water first, add the acid slowly with stirring, then top up to the final volume.
Worked example
To make 1,000 mL of 1 M acid from 12 M stock: V(acid) = 1 × 1,000 ÷ 12 = 83.3 mL. Place roughly 917 mL of water in the flask, add the 83.3 mL of acid slowly, then adjust to the 1,000 mL mark.
Frequently asked questions
Why add acid to water and not the reverse?
Mixing concentrated acid and water is strongly exothermic. Adding a little acid to a large volume of water lets the water absorb the heat safely. Adding water to acid concentrates the heat in a small volume that can boil violently and spray corrosive droplets — the classic lab-safety reason for "do as you oughta, add acid to water".
Do I add exactly the calculated water first?
Add most of it first, dilute the acid into it, then bring the solution up to the final volume mark. Because mixing changes the total volume slightly, finishing to a fixed final volume is more accurate than pre-measuring both parts.
Does this handle percent-based acids?
This tool works in molarity. For weight-percent stocks, convert to molarity first (using the density and molar mass) or use a dilution-by-percent tool; the C₁V₁ = C₂V₂ balance itself is identical in any consistent concentration unit.
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This calculator is for educational purposes. Double-check important results before acting on them.