Concentrated Acid/Base Dilution
Make a working solution from a concentrated reagent. Pick the acid or base (or enter your own assay % and density), set the molarity and volume you need, and get the exact volume of concentrated stock to measure — with the always-add-acid-to-water recipe.
How to use this tool
Concentrated reagents are sold by mass percent (assay), not molarity. This tool converts the bottle's assay % and density into a molarity, then tells you how much to measure for your target.
What to enter
- Reagent: pick a common one to load its assay %, density and molar mass — or choose "custom" and read the three numbers off your bottle's label.
- Target molarity and final volume: the solution you want to make.
Reading the result
You get the stock's molarity, the volume of concentrated reagent to measure, and a numbered recipe. Always add the concentrated acid (or base) to the water, never the reverse — the dilution is strongly exothermic.
Worked example
Concentrated HCl is 37 % (ρ 1.19) ≈ 12.1 M. To make 1 M HCl, 1 L: measure 82.8 mL of concentrated HCl into ~900 mL water, then make up to 1 L.
Inputs
Dilution recipe
The stock molarity comes from the assay % and density on the bottle; the volume to measure follows C₁V₁ = C₂V₂. Add acid to water — never water to acid.
Methodology
A concentrated reagent's molarity is M = (assay% / 100) · ρ · 1000 / MW, where ρ is the density in g/mL and assay% is the mass fraction of the pure substance. The volume of stock to dilute is then V₁ = M₂V₂ / M₁ (C₁V₁ = C₂V₂), and the balance is water. Reference assay/density values are typical commercial grades; always confirm against your reagent's certificate of analysis.
Sources
- Merck/Sigma-Aldrich reagent specifications (typical assay and density).
- CRC Handbook of Chemistry and Physics — concentrated reagent data.
Known limits
- Assay and density vary by grade, lot and temperature; use your bottle's actual values for accurate work.
- Volumes are additive-approximate; for the most accurate molarity, make up to the final volume in a volumetric flask rather than adding a fixed volume of water.
- Safety guidance is general — consult the SDS for the specific reagent.