Source: Laboratory of Dr. Michael Evans — Georgia Institute of Technology

The ratio of the mass of a substance to its volume is known as the mass density or, simply, the density of the substance. Density is expressed in units of mass per volume, such as g/mL or kg/m³. Because the density of a substance does not depend on the amount of substance present, density is an “intensive property”.

To measure the density of a sample of material, both the mass and volume of the sample must be determined. For both solids and liquids, a balance can be used to measure mass; however, methods for determining volume are different for solids and liquids. As liquids can flow and take the shapes of their containers, glassware such as a graduated cylinder or volumetric flask can be used to measure the volume of a liquid. The volume of an irregularly-shaped solid can be measured by submersion in a liquid — the difference in volume caused by addition of the solid is equal to the volume of the solid.

This demonstration illustrates the methods for measuring the density of solids and liquids. Using a volumetric flask and an analytical balance, the density of ethanol can be determined. Using a graduated cylinder, analytical balance, and water as the displaced liquid, the density of zinc metal can be determined.

1. Determination of the Density of Liquid Ethanol

1. Place a clean and dry 50-mL volumetric flask on an analytical balance.
2. Press the “Tare” or “Zero” button on the balance. The balance should read 0.000 g.
3. Use a buret funnel to add 45 mL of liquid ethanol to the volumetric flask.
4. Use a Pasteur pipette to add the final 5 mL of liquid, just until the bottom of the liquid’s meniscus touches the marking on the flask.
5. Weigh the volumetric flask ag

Table 1 lists results for the determination of the density of ethanol using a 50-mL volumetric flask. Densities were calculated by dividing the measured mass by 50.0 mL. The mean measured density was 0.789 ± 0.001 g/mL. Table 2 lists results for the determination of the density of a sample of zinc metal using a 100-mL graduated cylinder and the liquid displacement method. Note that the measured densities are constant (within experimental error) for both substances. Table 2