3. Properties of Air
3. Properties of Air
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Demonstrate and explain some properties of air through simple experiments
Imagine you're standing outside on a hot day, and suddenly, a cool breeze brushes past your face. You can’t see it, but you can feel it! What was that? Was it something real or just your imagination? Well, it’s something we use every single day without thinking about it—air. But did you know that air can be very mysterious? It can lift heavy aeroplanes into the sky, fill balloons with colour, and even help fires burn. But here's the big question: if we can't see air, how do we know it's there? And what special powers does it have that make it so important to life on Earth? Today, we’re going to unlock some secrets about air and discover the amazing properties that make it so powerful!
a. Air is colourless, tasteless and odourless1
Air is colourless and lacks any natural colour. It doesn't even have a smell of its own. But occasionally, certain gases combine with air to give us a pleasant or unpleasant odour. Air also lacks taste.
Fig. 3.1 Air is odourless and colourless
Application: Since air is colourless, it helps us see our surroundings clearly. It doesn’t block our vision, and we can run, walk, or play without anything in our way.
Air being odourless helps us in several ways. It allows us to detect harmful or beneficial substances that have a smell, like smoke from a fire or the scent of flowers.
Air being tasteless is beneficial because it allows us to breathe without being distracted or overwhelmed by any strong or unpleasant flavours. Imagine if the air had a strong taste—it could interfere with our ability to enjoy food, affect our comfort, and make breathing uncomfortable.
b. Air is a mixture
We cannot see the air around us, but it is there.
So what actually is air?
It is an invisible mixture of many gases. Approximately 78% of the air in Earth's atmosphere is nitrogen, and 21% is oxygen. Small amounts of various other gases, including carbon dioxide, neon, and hydrogen, are also present in the air.
Fig. 2.1 Composition of Air
Although most of the air is gaseous, it also contains many microscopic particles, called aerosols. When the wind blows, some aerosols—like dust and pollen—are naturally swept up. Smoke, soot, and other particles from factories and vehicles also get carried by the air. These are the main causes of air pollution.
Fig. 2.3 Aerosols
Air Holds Water:
Air also consists of water vapour, which we can occasionally see as clouds. The water cycle enables water to enter the atmosphere.
Fig. 2.4 Water vapour in Air
It is necessary to keep track of long-term changes in water vapour since they are strongly related to other weather patterns and trends.2
c. Air can be compressed
Air has the amazing ability to be compressed significantly under pressure. You'd be surprised to know that all the air inside a space as large as a house can actually be pressed into a small tank3.
Air compressors are handy in both homes and industries, serving different purposes. A simple example is the hand pump used to fill up bicycle tires. In factories, compressed air is widely used for various tasks like spraying paint, vacuum packing, control elevators3.
Fig. 2.5 Diagram of air compressed by a pump
d. Air is affected by temperature
Another characteristic is its ability to expand. When air is heated, like most substances it expands and takes up more space4. On the other hand, when the air becomes colder it contracts and takes up less space. This is why a beach ball left in the garage overnight might appear "smaller" in the morning compared to when it was warmer during the day.
Watch this video to understand the effect of temperature on air.
Vid. 3.1 Air is affected by temperature6
Try this simulation to see the effect of temperature on gases:
Instructions for Exploring the Properties of Gas Using PhET Simulation
1. Open the Simulation:
Open the PhET simulation for "Properties of Gases" on your computer or tablet by clicking the link above.
2. Set Up Your Experiment:
Start with the default settings in the simulation.
Observe the gas particles moving inside the container.
3. Explore How Gas Fills Space:
Drag the plunger of the container to make the space bigger or smaller.
Watch how the gas particles move and spread out to fill the space.
4. Check How Gas Compresses:
Use the plunger to push down and compress the gas.
Notice how the particles come closer together.
5. Observe the Effect of Temperature:
Increase or decrease the temperature using the slider.
Watch how the speed of the gas particles changes.
6. Record Your Observations:
Use your notebook to write down what you notice about the behavior of gas when the space, temperature, or number of particles changes.
e. Air can diffuse
If you've ever walked into a kitchen where bread was baking, you probably noticed how the delicious smell filled the air. Well, the reason for that is because gases, like the ones creating the lovely bread aroma, can spread out and fill the space around them. Unfortunately, the same happens with unpleasant smells, like that of a rotten egg. The not-so-pleasant smell quickly moves through the room7.
Diffusion happens when particles in a substance move around and mix with another substance, spreading out in the process8.
Diffusion is a fundamental property of gases and is driven by the natural tendency of gas particles to move randomly and occupy available space.
Watch this video to understand what diffusion is:9
Vid. 3.2 Diffusion of gases
Glossary
mixture: a substance that is made by mixing other substances together
aerosols: any solid or liquid droplets suspended in the atmosphere
pollution: the introduction of harmful materials into the environment
compressed: to make something fill less space than usual
temperature: measure of hotness or coldness
diffuse: to (cause a gas or liquid to) spread through or into a surrounding substance by mixing with it
soot: Soot is black powder which rises in the smoke from a fire
pressure: the force that is produced when you press on or against something
Summary
Air is colourless, tasteless and odourless.
Since air is colourless, it helps us see our surroundings clearly.
Air is an invisible mixture of gases. It consists of about 78% nitrogen, 21% oxygen, and small amounts of other gases.
Air contains microscopic particles called aerosols like dust and pollen.
Air contains water vapour.
Water vapour can be seen as clouds, and the water cycle enables water to enter the atmosphere.
Air can be significantly compressed under pressure.
Air compressors are used for various purposes in homes and industries.
Air expands when heated and contracts when cooled.
Gases in the air can diffuse and fill the surrounding space.
Diffusion occurs when particles in a substance mix with another substance, spreading out in the process.
References
1.7 Properties of Air. Denwool, 2020, link
2 Galaxy A Course in Science Book 6>Air>Put on your thinking cap>Q 7, Embibe,(n.d) link
3 Air. Kids Britannica, n.d, link
4 Properties of Air. Denwool, n.d, link
5 Properties of Air. MRPO, n.d, link
6 How Does temperature Affect Air. Youtube, n.d, link
7 The Properties of Gases. Chemed, n.d, link
8 Diffusion in solids, liquids and gases. Physics Catalyst, n.d, link
9 Diffusion.Youtube, n.d, link
Extension
Read this to explore more about air: link
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