What is percentage by mass and volume?

Short Answer

Percentage by mass and percentage by volume are two methods used to express the concentration of a solution.
Percentage by mass tells how many grams of solute are present in 100 grams of solution, while percentage by volume tells how many millilitres of solute are present in 100 millilitres of solution.

These methods are simple and commonly used in laboratories, industries, food products, and household items to show how much of a substance is present in a mixture.

Detailed Explanation

Percentage by Mass and Volume

Percentage by mass and percentage by volume are two basic concentration units that describe how much solute is present in a solution. These methods use simple ratios and are widely used in chemistry because they are easy to calculate and understand. They also appear frequently in everyday life—for example, on labels of food, medicines, and cleaning products.

Both percentages express concentration in terms of “out of 100,” but they differ in whether mass or volume is used.

  1. Percentage by Mass (Mass Percent)

Percentage by mass, also called mass percent, expresses the concentration of a solute in a solution based on mass. It is defined as:

Percentage by mass = (mass of solute ÷ mass of solution) × 100

Key points:

  • Uses grams as the common unit
  • Mass of solution = mass of solute + mass of solvent
  • Represents how many grams of solute are present in 100 g of solution

Example:

If 10 g of salt is dissolved in 90 g of water:

Mass of solution = 10 + 90 = 100 g
Percentage by mass = (10 ÷ 100) × 100 = 10%

This means 10 grams of solute are present in 100 grams of solution.

  1. Percentage by Volume (Volume Percent)

Percentage by volume, also called volume percent, expresses concentration based on volume. It is commonly used for solutions involving liquids. The formula is:

Percentage by volume = (volume of solute ÷ volume of solution) × 100

Key points:

  • Uses millilitres or litres
  • Typically used when both solute and solvent are liquids
  • Represents how many millilitres of solute are present in 100 mL of solution

Example:

If 20 mL of ethanol is mixed with water to make 100 mL of solution:

Percentage by volume = (20 ÷ 100) × 100 = 20%

This means 20 mL of ethanol is present in every 100 mL of solution.

Difference between mass percent and volume percent

Even though both are percentages, they differ because:

  • Mass percent uses mass, which does not change with temperature.
  • Volume percent uses volume, which can expand or contract with temperature.

Mass percent is more accurate for solid solutes or temperature-sensitive mixtures.
Volume percent is commonly used for liquid–liquid mixtures such as alcohol–water mixtures.

Why percentage by mass and volume are useful

These concentration units are simple and practical. They are used in:

  1. Food industry

Labels such as “5% sugar” or “2% fat” use mass percent.

  1. Medicines

Topical creams and ointments show drug concentration as mass percent.

  1. Household products

Cleaning liquids often show volume percent of alcohol or disinfectant.

  1. Chemistry laboratories

Mass percent helps prepare solid solute solutions.
Volume percent is used for liquid mixtures.

  1. Industries

Chemical manufacturing uses both for quality control.

Temperature effect

  • Mass percent is not affected by temperature, because mass remains constant.
  • Volume percent changes with temperature, because liquids expand when heated and contract when cooled.

Therefore, when accuracy is important, mass percent is preferred.

Example calculations

Example 1: Mass percent

You dissolve 5 g of glucose in 45 g of water.

Mass of solution = 5 + 45 = 50 g
Mass percent = (5 ÷ 50) × 100 = 10%

Example 2: Volume percent

You mix 30 mL of liquid fragrance with water to make 150 mL of solution.

Volume percent = (30 ÷ 150) × 100 = 20%

Example 3: Real-life bottle labels

A hand sanitiser bottle may say 70% alcohol (v/v).
This means 70 mL of alcohol per 100 mL of solution.

Advantages of percentage by mass

  • Temperature independent
  • Useful for solid solutes
  • Highly accurate in scientific measurements

Advantages of percentage by volume

  • Easy to use for liquid mixtures
  • Common in consumer products
  • Convenient for volatile liquids like alcohol

Limitations

  • Volume percent becomes inaccurate with temperature changes.
  • Mass percent cannot be used easily when both solute and solvent are liquids of different densities.

Despite these limitations, both units remain widely used.

Conclusion

Percentage by mass and percentage by volume are simple ways to express the concentration of a solution. Mass percent measures grams of solute per 100 grams of solution, while volume percent measures millilitres of solute per 100 millilitres of solution. These units are widely used in chemistry, laboratories, industries, and everyday products. Understanding both helps in preparing solutions accurately and interpreting concentration labels on consumer goods.