Mass Percent
Concentration as a percentage by mass.
Formula
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Example
10 g in 100 g = 10%
How it works
Mass percent tells you what fraction of a mixture’s total mass comes from the solute, then converts that fraction into a percentage by multiplying by 100. It works because a percentage is just a ratio out of 100, so comparing solute mass to the full solution mass gives a standard way to express concentration. This is useful when the amount dissolved matters relative to the entire mixture, not just the amount of liquid or solvent.
When to use it
Use this formula when you are given or need to find the concentration of a solution by mass, such as in saltwater, alloys, or lab mixtures. It is also common in chemistry problems involving solid or liquid components where the total mass of the mixture is known.
Worked example, step by step
A sugar solution has 8 g of sugar dissolved in 92 g of water. Step 1: Find the total mass of the solution: 8 g + 92 g = 100 g Step 2: Substitute into the formula: % = (m_solute / m_solution) × 100 Step 3: % = (8 / 100) × 100 Step 4: % = 8% Final answer: The mass percent of sugar is 8%
Common mistakes to avoid
- Using the mass of the solvent instead of the total mass of the solution
- Forgetting to multiply by 100 at the end
- Mixing up solute and solution and reversing the ratio
Did You Know?
Mass percent tells you that seawater is about 3.5% salt by weight, guiding everything from cooking to chemistry.
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