Density (d) is an intrinsic physical property that is calculated by dividing the mass of an object by its volume. The equation for calculating a density, based on its definition, can be written as
Since the quantities in the numerator and denominator must have different units, unit cancelation cannot occur. Therefore, the unit for density must include both a mass unit and a volume unit, expressed in a fractional format. Masses of objects are typically measured in grams (g), and volumes can be reported in either milliliters (mL) or cubic centimeters (cm3). As a result, density can be calculated in both metric (grams per milliliter, g/mL) and SI (grams per cubic centimeter, g/cm3) units.
An intrinsic property is defined as a quantity that does not change, regardless of the amount of substance that is present. Density is a property of the material itself, so each unique substance has its own corresponding density, which can vary slightly with temperature. For example, liquid water has a density of 1.00 g/mL (or 1.00 g/cm3), regardless of the quantity of water being studied. (Since water is such a common and versatile chemical, most chemistry instructors encourage students to memorize as many facts about water as possible. The density of liquid water is the first such quantity that you should commit to memory.) The densities of four common liquids are shown below in Table \(\PageIndex{1}\).
Table \(\PageIndex{1}\): Densities of Four Common Liquids
Substance
Density at 25°C (g/cm3)
corn oil
0.922
liquid water
1.00
honey
1.42
mercury
13.6
Intrinsic properties are non-intuitive, as most people associate having a greater amount of a substance with larger numerical values. Quantities that do scale with the amount of substance that is present are called extrinsic properties.