How to Calculate Composite Density

By Brian Baer
Different liquids can have different densities.

The composite density, or solution density, refers to the total density of a chemical mixture or composition of materials. Density is the mass of a substance per unit volume such as pounds per gallon. Every substance has an individual density which is dependent upon temperature. If multiple substances are mixed into a homogeneous solution, the composite or solution density can be found by multiplying each substance’s density by its solution concentration.

Determine the substances (species) to be mixed into a solution. For instance, 2 lb. of species A is added to 3 lb. of species B and 4 lb. of species C. The total solution mass is 9 lb. and the mass concentration (mass fraction) of each substance is 0.22 (A), 0.33 (B) and .045 (C). The sum of the mass fractions should always equal 1.0.

Determine the density of each component in the solution. For instance, species A has a density of 7.5 lb. per gallon, species B has a density of 8.3 lb. per gallon and species C has a density of 9.1 lb. per gallon.

Determine the solution density using the mass fractions and densities of each component. This is done with the equation (density A x 0.22) + (density B x 0.33) + (density C x 0.45). The answer is 8.484 lb. per gallon.

About the Author

Brian Baer has been writing since 1982. His work has appeared on Web sites such as eHow, where he specializes in technology, management and business topics. Baer has a Bachelor of Science in chemical engineering from the University of Arkansas and a Master of Business Administration from the University of Alabama, Huntsville.