Solution Preparation Calculator
Calculate how much solid to weigh or how much concentrated reagent to measure for a solution at the required final concentration and volume.
Preparing a solution
The calculation depends on the starting material. A solid requires molar mass and purity; a commercial concentrated solution requires its wt% concentration, density and molar mass. The calculator also returns a short bench procedure and a numerical consistency check.
From a solid solute
Enter the required final concentration and flask volume. Purity corrects the actual mass that must be weighed.
From a concentrated or commercial solution
Select a common reagent or enter the data from your bottle. Assay and density remain editable: the label, CoA or SDS for the material you are actually using takes precedence over the preset.
Equations used
For a solid solute, the required pure-solute mass follows from the requested concentration and final volume. For molar concentration:
\[m_{pure}=c\,V_f\,M\qquad m_{weigh}=\frac{m_{pure}}{p}\]
where \(p\) is purity as a fraction. For a commercial solution specified by mass fraction, stock molarity is:
\[c_{stock}=\frac{1000\,\rho\,w}{M}\]
with \(\rho\) in g/mL and \(w\) as a mass fraction. The amount of stock is calculated from the required solute amount; it is not found by simply subtracting volumes.
Why the calculator does not report “water to add”
Correct volumetric preparation does not generally mean subtracting the stock volume from the final volume. Transfer the calculated amount of solid or stock solution, then make up to the final mark. This calculator therefore does not assume additive volumes and does not attempt to model contraction or expansion on mixing.
Built-in concentrated reagents
The preset list includes several common teaching-lab reagents: hydrochloric, sulfuric, nitric and phosphoric acids, glacial acetic acid, ammonia solution and hydrogen peroxide. The values are documented starting points, not replacements for the container label: assay and density can vary with grade, supplier, temperature and lot.
Ammonia solution
Commercial ammonia solutions are usually specified as a mass percentage of NH₃ in water. Do not enter the molar mass of NH₄OH in this calculator: the reference solute here is NH₃. Density is below that of water and ammonia is volatile, so use the assay and density stated for the material actually in the lab.
Hydrogen peroxide
The hydrogen-peroxide preset uses wt% H₂O₂. Some consumer and technical products instead state concentration in “volumes”; that value is not a mass percentage and must not be entered directly in the wt% field. Conversion from peroxide “volume strength” is deliberately outside this calculator.
Bench and safety note
The calculator determines quantities and volumes; it does not replace the SDS, local SOP, PPE or instructor directions. For concentrated reagents always verify identity, assay, density and reference temperature. When a laboratory procedure calls for dilution of a concentrated acid, follow the local SOP and add reagent to water, not water to reagent.