Understanding The Density Of Solids, Liquids And Gases

One of the most common ways of comparing different materials is by looking at their density. In school laboratories, there are many experiments which will investigate the differences in density between solids, liquids, and gases by looking closely at the distance between the particles.

The EduLab Science Squad are experts in school laboratory experiments, and have put together this article to help teach students the density of solids, liquids, and gases, and how to calculate this.

What Is Density?

Density measures the particles in a substance and looks at how compact the mass of an object is. When two different materials are combined together, density determines which will sink and which will rise. Understanding the density of solids, liquids, and gases, and how they interact with each other is a critical step to understanding the planet we live on and the world around us.

Solids and liquids are made up of particles which are very close together. Solid state objects can often be melted to liquids, but because the particles still remain close there is usually just a small volume increase. A mass of liquid which is the same as a mass of solid will have a slightly greater volume due to the change in density. To compare, the density of liquid iron is 6.9 g/cm3, whereas the density of solid iron is 7.8g/cm.

Liquids can change state further by being evaporated to a gas state. Gas states have particles which are very far apart and move freely, causing the volume to increase greatly. A mass of gas will have a much larger volume compared to the same mass of liquid. This is because it has a much lower density. The density of gaseous oxygen is 0.0014 g/cm3, compared with liquid oxygen which has a density of 1.1 g/cm3.

Put simply, solid masses have a high density as particles are very close together, liquid masses are slightly less dense, and gas masses have a very low density with particles much further apart. Many materials can change between states with processes such as freezing, condensation, evaporation, and melting.

Experiments To Understand Density

Density can be a confusing subject to understand, and the easiest way to teach this concept to students is through experiments. There are many lab experiments available which demonstrate density to students in a clear manner. Here are our top three laboratory experiments to understand the density of solids, liquids, and gases.

The Density Tower

Creating a density tower is a simple yet powerful way to demonstrate the density of different materials. You will form a tower of various liquids to teach students how they each have a different density and how they interact together. You will need:

• A concentrated washing up liquid
• Light corn syrup
• Water
• An alcoholic spirit
• Canola oil
• A clear glass beaker

Start by pouring the light corn syrup into the bottom of the beaker, followed by a layer of washing up liquid, a layer of water, a layer of alcoholic spirit, and finally a layer of canola oil. If you want to make each layer really stand out, add a drop of food colouring to each liquid as you go. Students will be able to clearly see the distinct layers of liquid, revealing how each has a slightly different density.

Hot vs Cold

In this experiment, you can show how temperature can change the density of a material. You will need two glass beakers, a Bunsen burner, food colouring, water, and ice. Fill each beaker with 150ml of water and add blue food colouring to one and red to the other. In the blue beaker, add some ice and place it in a fridge for a few minutes. Use the Bunsen burner with a tripod and gauze to slowly heat the red beaker, but make sure it doesn’t reach boiling point. Add a few pipets of blue water to a cylinder, and then carefully add drops of red water and watch the results.

Distillation

Distillation experiments are a very popular way of demonstrating density in different components. Materials can be separated using different boiling points, and gases can be removed from liquid mixtures easily. For a distillation experiment you will need distillation apparatus and a liquid mixture to separate. Read our article on how to set up distillation apparatus and use this experiment to show the differences between liquids and gases.