Percent Solution Preparation Calculator
Making a % (w/v) reagent — say a 10% sodium thiosulfate solution for chlorine-demand testing? Enter the target strength and volume and get the exact grams to weigh, corrected for the purity on your reagent bottle.
Reagent Mass
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How the calculation works
Formulas
% (w/v) = grams of solute per 100 mL of final solution
Grams (100% basis) = % × volume (mL) / 100
Grams to weigh = grams (100% basis) / (purity / 100)
Dissolve in part of the water, then bring to the final volume in a volumetric flask.
% (w/v) = grams of solute per 100 mL of final solution
Grams (100% basis) = % × volume (mL) / 100
Grams to weigh = grams (100% basis) / (purity / 100)
Dissolve in part of the water, then bring to the final volume in a volumetric flask.
Notes & limitations
Percent weight/volume is defined as grams of solute per 100 mL of final solution (Standard Methods for the Examination of Water and Wastewater, Section 1010 on reagent preparation). Dividing by the fractional purity corrects for assay strength stated on the reagent label.
- This is % w/v (solids in liquid). For % v/v (liquid in liquid) use volumes directly; for % w/w you need the solution density.
- Always add solute to part of the water and dissolve fully before bringing to final volume — never weigh into a full volume of water.
- Check the SDS for each reagent; some concentrated preparations generate heat or fumes.
- Label every bottle with chemical name, concentration, prep date, and preparer initials per your lab QA plan.
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