Beginner Topic 885 of 1102 Analytical, Lab & Spectroscopy
Density
Mass per unit volume, an intensive property that identifies substances.
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In-depth explanation of Density
Density is the mass per unit volume of a substance, d = m/V, usually expressed in g/mL, g/cm3 or kg/m3. It is an intensive property, so it does not depend on the amount of material present, which is why it helps identify a pure substance. Density changes with temperature because most materials expand when heated, so values are quoted at a specified temperature. An object floats if its average density is less than that of the surrounding fluid, which is the principle behind hydrometers and density-based separations. Liquid densities are measured with a pycnometer or by weighing a known volume, and solid densities can be found by displacement of water. Water has a density of about 1.000 g/mL at 4 C, its value at maximum density.
Going deeper: Density
Key ideas: Rearrange d = m/V to find mass or volume. Convert 1 g/cm3 to 1000 kg/m3. For a mixture, total mass over total volume gives the average density, but volumes are not always additive for liquids. Water displacement gives volume of an irregular solid, with density equal to mass divided by the rise in volume. Ice (0.917 g/cm3) floats on water.
Common mistakes and connections: Students confuse density with weight or assume a larger sample has higher density. Reading a meniscus incorrectly or trapping air bubbles on a displaced solid gives errors. Temperature must be stated because density changes with it. Links to specific gravity, hydrometers, gas density from the ideal gas law (d = PM/RT) and separations by flotation.
Visualization of Density
Density is mass per volume and identifies materials: gold at 19.3 g/cm3 is far denser than water at 1.00, so a 100 mL gold bar weighs 1.93 kg. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Gold has a density of 19.3 g/cm3, so a 100 mL gold bar would weigh 1930 g, or 1.93 kg.
Frequently asked questions about Density
What is Density?
Mass per unit volume, an intensive property that identifies substances.
Is Density a beginner, intermediate or advanced topic?
Density is a beginner topic in Analytical, Lab & Spectroscopy. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Density?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Accuracy and Precision, Scientific Notation, Dimensional Analysis.
What comes after Density?
The next topics in Analytical, Lab & Spectroscopy are Percent Composition and Empirical Formula.
Can I practise Density with quizzes?
Yes. The interactive lesson includes a self-check question on Density, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Density fits in Analytical, Lab & Spectroscopy
Density is topic 9 of 99 in Analytical, Lab & Spectroscopy.