Specific Gravity

Definition and Formula

Specific gravity is a dimensionless quantity that compares the density of a substance to the density of water at the same temperature. It is commonly used in chemistry to characterize liquids and solids.

• Formula:

• Unitless: Since both densities are measured in the same units, specific gravity has no units.

• Temperature Dependence: The density of water changes with temperature, so specific gravity values depend on the temperature at which measurements are made.

Densities of Water at Different Temperatures

The density of water varies with temperature. The following table summarizes water densities at selected temperatures:

Application Example

Example: If the specific gravity of sulfuric acid is 1.27 at room temperature (25°C), what is its mass (in mg) for 2.3 L?

• First, calculate the density of sulfuric acid using the specific gravity and the density of water at 25°C:

• Convert 2.3 L to mL:

• Calculate mass:

Practice Problems

Calculating Specific Gravity and Mass

• Practice 1: What is the specific gravity of lithium metal (in g/mL) at 10.0°C if a cube measures 0.82 cm × 1.45 cm × 1.25 cm and has a mass of 0.794 g?

  • Calculate volume:

  • Density:

  • Density of water at 10°C:

  • Specific gravity:

• Practice 2: Ethyl alcohol has a specific gravity of 0.7892 at 10°C. What is the volume of 250 g of ethyl alcohol?

  • Density of ethyl alcohol:

  • Volume:

Key Terms

• Density: Mass per unit volume, typically expressed in g/mL or g/cm3.

• Specific Gravity: Ratio of the density of a substance to the density of water at the same temperature.

• Unitless Quantity: Specific gravity has no units because it is a ratio of two densities.

Summary Table: Specific Gravity vs. Density