Science at Home - Air Has Mass - Eva Varga

July 25, 20131

I’m excited to participate in my first Google+ event … Science at Home.  This month, the topic is Air and I have put together two activities that I know you will enjoy, both of which I have used with my own kiddos.  The focus of the demonstrations is to show that air has mass.  When doing these activities with your children, however, try not to reveal the objective of the demonstration.

Allow students to observe the process without knowing the outcome.  This will help them to write their own title and objectives. Instead of standard after-lab-questions, ask students to complete the missing title and objectives. It is a fun twist and makes the lab more creative and inquiry based.

Air is the sea of particles in which we live. Wrapped around us like a blanket, students sometimes mistake air as being without mass or weight. I shared two science demonstrations today to prove to students that air does indeed have mass.

Air Has Mass

In the first activity, two balloons filled with air, will be used to create a balance.  Inflate the two balloons until they are equal in size and tie them off. Attach a piece of string to each balloon. Then, attach the other end of each of the strings to the opposite ends of the meter stick, keeping the balloons the same distance from the end. The balloons will now be able to dangle below the ruler.

Tie the third string to the middle of the meter stick and hang it from the edge of a table or support rod. Adjust the middle string until you find the balance point where the meter stick is parallel to the floor. Once the balance scale set-up is completed, the experiment can begin.

As the kids sketch the set-up, ask them to predict or make an hypothesis about what will happen if you were to poke a hole in one balloon.  Do so and encourage them to record their observations in words or pictures in their journal.

The balloon that remains full of air will cause the ruler to tip showing that the air has weight. The empty balloon’s air escapes into the surrounding room and is no longer contained within the balloon. The compressed air in the balloon has a greater weight than the surrounding air. While the weight itself cannot be measured in this way, the experiment gives indirect evidence that air has mass.

CO2 is Heavier than Air

Another fun demonstration you can do easily at home illustrates that carbon dioxide gas is heavier than air. It takes a little practice but once you’ve got it down it’s pretty fun!  You’ll need two glasses, baking soda, vinegar, and a small candle.  Measure a tablespoon of baking soda into one glass.  Light the candle.  Measure a tablespoon of vinegar and pour it into the glass with the baking soda.  Allow it to bubble for a moment and generate the carbon dioxide gas.  Depending upon the size of your glass, it may bubble over.  No worries.

When the bubbles have receded a little, carefully lift the glass and pour the carbon dioxide gas into the second glass.  Be careful not to pour the liquid; you won’t actually see anything pour – but trust me.  Then, gently lift the second glass (which appears to be empty) and pour it over the burning flame. In just a few seconds, the flame will be extinguished.

In order to burn, fire requires oxygen. Fires start when a flammable material, in combination with a sufficient amount of oxygen gas (or another oxygen-rich compound), is exposed to a source of heat, and is able to sustain a rate of rapid oxidation that produces a chain reaction (the fire tetrahedron).  Fire cannot exist without all of these elements in place and in the right proportions.  When the carbon dioxide gas is poured from the glass, gravity pulls it down and it pushes the oxygen rich air away.  Without oxygen, the flame is extinguished.

Take it Further

Can you find ways to test the mass of different gases?  How could you compare the mass of helium and carbon dioxide?  What can the periodic table tell you about these elements?

In addition to two activities I shared in the hangout today, I also did a few other simple activities with my kiddos which I have described in more detail in an earlier post, Air Pressure and Wind Activities.

If you missed the hangout on Google+, you can see the full video recording at Science at Home.

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