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Mass of Gases
In some previous lessons we have gone over mass and density differences in solids, liquids, and gasses. (Mass= Density x volume) We have looked at the relative density of solid objects, but this lesson goes over gases with different masses. For this lesson we watched several clips from science demonstrations by Dr. Shakhashiri. He was my chemistry professor for freshman chemistry. Every year he does a science demonstration show, and you can find detailed explanations of the experiments that he does on his website and in his books.
The first thing I went over in this class was that air was made up of molecules, and these air molecules have different masses. That is why a helium filled balloon floats, and why carbon dioxide will stay in a beaker for a while after it sublimates from a solid state. Helium has the lowest atomic mass after hydrogen. A carbon dioxide molecule has a higher mass than air, because air is mostly made up of less massive molecules of nitrogen and oxygen. Here are some video clips that demonstrate that.
Air bubbles floating on carbon dioxide gas (5:25-7:20)
Carbon dioxide pouring over and extinguishing flames (12:15-13:34)
Moving Air
The next thing we talked about was moving air. In the following video we see moving air holding a balloon up, and also how moving air can fill a very large plastic bag quickly. First, I explained the Bernoulli principle so the children understood what Dr. Shakhashiri was saying in this clip.
Moving air holding up a balloon and moving air filling a large bag (59:59-1:11:30)
Foam
A foam is a solid or liquid with bubbles of gas in it. We had talked about how foam is able to float on water because it is less dense in a previous class when we made a compass. In this video the scientist makes a foam and also dissolves a foam in acetone.
Making a foam and dissolving a foam (45:30-51:05)
In the video Rodney mentions that cake is a foam. I made some cake for the kids to look at (and then eat). I made two cakes, one with baking powder which supplies the acid and the base for the leavening. The other cake is made with baking soda (base) and vinegar (acid).
I mixed baking powder in water with vinegar to show the kids the bubbles that form. If you are at home or have access to an oven, you could have the kids actually make the cake. One other nice thing about this recipe is that there are no nuts, eggs, or dairy in it so most of the kids should be able to eat it. The recipe I used was for Wacky Cake from the book “America’s Best Lost Recipes”.
This cake must be put in the oven immediately after you mix the wet and dry ingredients. You can see how I made holes in the dry ingredients to put the oil, vinegar, and vanilla in. You poor the water all over the top, mix and put in a warm oven. This reaction of the vinegar and baking soda goes really fast, so if you leave the batter out for a while, the cake won’t rise properly.
Newton’s Laws of Motion
We had gone over Newton’s second law in our class the week before. This video clip goes over Newton’s first and third laws.
Newton’s First and Third Laws of Motion (51:05-end)
For more STEAM activities, take a look at my Pinterest board.