Mass Percent

In-depth explanation of Mass Percent

Mass percent is a concentration expressed as the mass of solute divided by the mass of the solution, multiplied by 100. It is a convenient unit for commercial and household products whose composition is given on the label, and it does not require molar masses. Because it is based on mass, it does not depend on temperature in the way that volume-based units do. Mass percent can be converted to molarity if the solution density and the molar mass of the solute are known. The unit is widely used to state the concentrations of acids and bleach.

Going deeper: Mass Percent

Key ideas: Formula: percent = (mass solute / mass solution) x 100. Mass of solution = solute + solvent. To get molarity: M = (percent x 10 x density) / molar mass; for 37 percent HCl with density 1.18 g/mL and M = 36.5, M is about 12. Volume percent and mass-volume percent are different, for instance 70 percent v/v ethanol.

Common mistakes and connections: Common errors are dividing by the solvent mass rather than the solution mass, and assuming 1 g/mL density for concentrated solutions. Another is treating percent concentration as additive by volume. Mass percent stays fixed with temperature. Links to molarity, molality, density and dilution of stock reagents.

Visualization of Mass Percent

Mass percent = mass solute / mass solution x 100; physiological saline is 0.9% NaCl, so 100 g contains 0.9 g salt. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Commercial vinegar is typically about 5 percent acetic acid by mass, meaning 5 g of acid per 100 g of solution.

Where Mass Percent fits in States of Matter & Solutions

Mass Percent is topic 78 of 109 in States of Matter & Solutions.

Related topics

• Like Dissolves LikeBeginner
• MolarityBeginner
• MolalityIntermediate
• Parts Per MillionBeginner
• NormalityIntermediate
• DilutionBeginner

Browse all 109 topics in States of Matter & Solutions