Rather than describing concentrations of solutions in terms of molarity, some solutions are described and prepared as percent solutions or percentages.
The most commonly used percent solution is percent weight by volume or %(w/v), whereby the mass of the solute is measured and the volume of the solvent is measured. The percent weight by volume is usually calculated by the grams of the solute divided by 100 units of the solvent (usually 100 mL). This is displayed in Step 1 of the provided example. By understanding this, you can then solve for either the % solution, solute (e.g., grams), or solvent (e.g., milliliters). The images walk you through performing one of these problems with two different methods.
Additional examples of how to interpret and interconvert percent solutions:
- 25% solution of KOH in water would contain 25 grams of KOH per 100 mL of water.
(25 g/100 mL) x 100% = 25%
- 15 grams of NaCl would be needed to create a 30% solution of NaCl in 50 mL water.
(15 g/50 mL) x 100% = 30%
- If 10 grams of Ca3(PO4)2 were weighed out, 200 mL of water would be needed to make a 5% solution of Ca3(PO4)2 in water.
(10 g/200 mL) x 100% = 5%
