Prepare a solution

How it is calculated

% w/v: grams = % × volume (mL) ÷ 100 = % × 10 × volume (L). g/L: grams = g/L × volume (L). mol/L: grams = mol/L × volume (L) × molar mass. % w/w: grams = % × final mass (g) ÷ 100, and water = final mass − reagent weighed.

Purity correction: reagent = pure solute ÷ (purity ÷ 100).

Example: 0.5 L of 1 mol/L NaOH with 98 % caustic soda. Moles = 1 × 0.5 = 0.5 mol; pure solute = 0.5 × 40.00 = 20 g; reagent = 20 ÷ 0.98 = 20.41 g.

Example: 500 g of 10 % w/w brine with pure salt. Salt = 10 × 500 ÷ 100 = 50 g; water = 500 − 50 = 450 g (450 mL).

Example: 1 L at 0.9 % w/v. Salt = 0.9 × 10 × 1 = 9 g, dissolved and made up to 1 L.

Keep in mind

• For concentrations by volume (% w/v, g/L, mol/L) the volume is that of the finished solution: dissolve in less water and make up to the mark in a volumetric container.
• Check whether the reagent is hydrated: copper sulfate pentahydrate (CuSO₄·5H₂O, 249.69 g/mol) does not weigh the same per mole as the anhydrous salt (CuSO₄, 159.61 g/mol). Use the molar mass of what you are going to weigh.
• Caustic soda and caustic potash absorb moisture and CO₂ from the air: if the container stays open for a long time the real purity drops. Keep it tightly closed.
• The purity correction assumes the impurities are inert. For solutions for medical or analytical use, check with a pharmacist or a chemist: this calculator does not replace a validated procedure.
• Dissolving caustic soda or sulfuric acid releases a lot of heat: add the solid or the acid to the water, little by little, with goggles and gloves.