Density of Solids, Liquids and Gases – Lesson Summary

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Learning Objective

In this lesson we will look more closely at density as a physical property, including what happens when substances with different densities are combined.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe density.
  • Express density as a mathematical relationship between mass and volume.
  • Calculate the density of regular and irregular solids.
  • Describe and explain the layering of substances with different densities.
  • Explain how temperature and pressure can affect the density of a substance.

 
density of solids liquids and gases lesson contents

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Lesson Topics

1 | Density

2 | Calculating Density

3 | Comparing Densities of Solids, Liquids and Gases

4 | Density Layering

5 | The Effect of Temperature on Density

6 | The Effect of Pressure on Density of Gases

7 | Summary

Lesson Summary

  • Density refers to how much matter is in a given amount of space.
  • It can be expressed mathematically as:
  • density formula word mass volume
  • where mass is the amount of matter in the substance and volume is the amount of space the substance occupies.
  • Density is measured in units such as g/cm3 or kg/m3.
  • The mass of a substance can be determined by weighing it on an electronic balance.
  • The volume of a liquid can be determined by measuring it in a measuring cylinder.
  • The volume of a regular solid can be determined using a mathematical formula.
  • The volume of an irregular solid can be determined by measuring how much liquid it displaces in a measuring cylinder.
  • Volumes measured in mL can be converted to cm3 using the formula:
  • convert mL to cm3
  • Generally:
  • Solids generally have high or very high densities.
  • Liquids generally have high densities.
  • Gases generally have very low densities.
  • Mixtures containing substances with different densities will form vertical layers, where:
  • The least dense substance will lie at the top.
  • The most dense substance will lie at the bottom.
  • Pure water has a density of 1 g/cm3.
  • Therefore, any substance with a density less than 1g/cm3 will float in water and any substance with a density greater than 1g/cm3 will sink in water.
  • Most frozen solids will sink in a liquid of the same substance as substances are usually more dense as solids than liquids.
  • Ice is unusual because it is less dense than water and therefore floats in it.
  • Heating substances causes them to expand and therefore become less dense.
  • Cooling substances causes them to contract and therefore become more dense.
  • Pressurising gases causes them to contract and therefore become more dense.

 
floating buoy buoyancy density

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(Header image: photoeverywhere, Adobe Stock)