1.7: Density

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Learning Objectives

Define density.
Determine the density of various substances.

Density (\(\rho\)) is a physical property found by dividing the mass of an object by its volume. Regardless of the sample size, density is always constant. For example, the density of a pure sample of tungsten is always 19.25 grams per cubic centimeter. This means that whether you have one gram or one kilogram of the sample, the density will never vary. The equation, as we already know, is as follows:

\[\text{Density}=\dfrac{\text{Mass}}{\text{Volume}} \nonumber \]

or just

\[\rho =\dfrac{m}{V} \nonumber \]


Substance	Density at 25°C (g/cm3)
blood	1.035
body fat	0.918
whole milk	1.030
corn oil	0.922
mayonnaise	0.910
honey	1.420

Notice in Table \(\PageIndex{1}\) that corn oil has a lower mass to volume ratio than water. This means that when added to water, corn oil will “float.”

Density can be measured for all substances, solids, liquids and gases. For solids and liquids, density is often reported using the units of g/cm³. Densities of gases, which are significantly lower than the densities of solids and liquids, are often given using units of g/L.

Example \(\PageIndex{1}\): Ethyl Alcohol

Calculate the density of a 30.2 mL sample of ethyl alcohol with a mass of 23.71002 g

Solution

\[\rho = \dfrac{23.71002\,g}{30.2\, mL} = 0.785\, g/mL \nonumber \]

Exercise \(\PageIndex{1}\)

Find the density (in kg/L) of a sample that has a volume of 36.5 L and a mass of 10.0 kg.
If you have a 2.130 mL sample of acetic acid with mass 2.234 g, what is the density in g/mL?

Answer a: \(0.274 \,kg/L\)
Answer b: \(1.049 \,g/mL\)

Summary

Density is defined as the mass of an object divided by its volume.

Contributors and Attributions

Marisa Alviar-Agnew (Sacramento City College)
Henry Agnew (UC Davis)