Home School Life Journal

Home School Life Journal ........... painting by Katie Bergenholtz
"Let us strive to make each moment beautiful."
Saint Francis DeSales

Chemistry, Lesson 2: Moving Matter

States of Matter
The concept that matter has different states and these states all have different properties can be taught from a really young age.

Solids

Rates of Freezing

Salt Lapbook

We have looked at the way in which salt affects the rate at which water freezes. In a liquid state, the molecules of the water have a significant amount of energy. They are free to move around, so they are constantly traveling around their container. To get into a solid state, the molecules have to slow down and stop moving around as much. The only way this can happen is to take energy away from the molecules. As a substance cools, its molecules lose energy. As they lose energy, they start to slow down until eventually they lose enough energy so the they almost stop moving around altogether. At that point the liquid turns into a solid. Well, when the salt is added to the water, the salt molecules also begin moving around in the water. Since the water molecules are attracted to the salt molecules, a chase ensues. The mutual attraction between the two adds more energy. Thus, in order for to get all of the molecules to slow down and stop moving, more energy must be removed. The only way this can happen is by lowering the temperature further. This is called freezing-point depression. This is why they put salt on icy roads and steps in the winter and why the salt helps make ice cream freeze when you are making it. It lowers the freezing point.


We also experimented with what substances freeze the fastest under the same temperatures.We put 1/4 cup of hot water into three other cups. To the first one we then added 1/4 cup of table salt, and to the second we added 1/4 cup of Epsom Salts. The third cup we left with just the water. To the fourth cup we put 1/4 cup of rubbing alcohol in.  To the fifth cup, we put 1/4 cup of Jello with hot water added to make a liquid. Next they had to hypothesize the order in which the liquids would freeze. We checked the cups every hour throughout the rest of the day. Cups Two and Three froze first. It was somewhat difficult to tell exactly when the Jello froze solid and when it was just thickened. The fourth cup froze last. This is to illustrate that different substances have different freezing points.
Alcohol, on the left, never froze, even after 24 hours, but the Jello, on the right, froze solid.

Liquids

There is no better way to examine liquids and their properties than giving them some mystery liquids to explore. I chose four liquids that were either clear or nearly clear: liquid hand soap, baby oil, canola oil and corn syrup. The first thing they did was explore the properties of the mystery liquids, comparing and contrasting them. (The Homeschool Scientist has a great Properties of Liquids worksheet you can print out to use with this exploration, if you wish.) I introduced the term, "viscosity" which is best described by experience. You can say that it is a way to describe a liquids movement against gravity, but they will probably be most contented to think of it as the liquid's thickness. The boys ranked the liquids from the one with the most viscosity, to the one with the least. There was some differences of opinion, and that was okay with me. Now, with this in mind, I brought out the containers of the real liquids and had them match them up by what they had observed from handling the test tubes of liquids.

Next, we decided to see how the liquids responded in experimenting environment to see if what they had observed about the liquid held true. I put one cup of flour in four bowls, one for each liquid we were exploring. I labeled each bowl with the liquid's name and they began by adding two Tablespoons of each liquid to the bowls. We kept adding more of the liquid until it formed a pleasing dough to play with. They quickly noticed that the more viscous the liquid, the more tablespoons they needed to mix in in order to make a dough. They ended up adding 6 Tablespoons to the Corn Syrup, 5 Tablespoons to the Liquid Soap, 4 Tablespoons to the Vegetable Oil and 3 Tablespoons to the Baby Oil.

Non-Newtonian Fluids

Concoctions For Play: Oobleck
We have made, played with and experimented with the mixture of cornstarch and water many times over the years and we have discussed the term "Non-Newtonian Fluid" in connection with the mixture. A liquid like this is called a non-Newtonian fluid because it does not follow the rules that Newton discovered most liquids follow. A non-Newtonian fluid has properties of both a solid and a liquid and reacts to stress with increased viscosity. Cornstarch (amylose) and water can be considered a colloidal suspension. A colloidal suspension is a two-phase system in which the starch and water are not dissolved but simply mixed into a permanent suspension that will not settle on standing.

Drops

Raindrops and Oil Drops, May 2008
The boys have experimented before with the properties of two liquids, water and oil, comparing and contrasting drops of both liquids on a piece of wax paper. Drops are made possible by the fact that liquids have atoms that tend to stay close to each other.

Surface Tension

Liquids in Space
Surface tension forms a like of skin in space that holds liquids together in spheres. Earth's gravity is strong enough to squash these spheres into ovals. I reminded them of a demonstration that we did that showed how liquids look in free fall and how gravity flattens them and breaks surface tension.

Gas

A Chemical Reaction

The classic baking soda and vinegar demonstration can be used to show voluminous expanding gas. Because the gas, caused by the chemical reaction, needed more space, it pushed against the balloon, causing the balloon to inflate with the expanding gas. The gas molecules put pressure against the sides of the balloon.

Changing States of Matter

There are many simple ways to show changing states of matter. Perhaps the simplest one is to make some Jello. It begins as a powder, or solid. Water, a liquid, is added to the Jello, but not before some of it turns into steam, a gas by the physical change of the water's boiling. Once the hot water is added, the Jello powder turns into a liquid as well as it dissolves. Putting the Jello liquid into the refrigerator, chilling it, by physical change, turns the Jello back into a solid.
You can also look at the changing states of matter by dissolving lollipops in some hot water and seeing the solid change into a liquid. Take this liquid and pour it into an Popsicle mold and pop them into the freezer and you will see your liquid turn back into a solid as it freezes, and make a tasty summertime treat as well, but be careful to eat them before they change back into a liquid state! We talked about how temperature can affect the changing states of matter.


You can demonstrate the water cycle by using a pot with a small amount of water in it, a zippered sandwich bag full of ice and a bowl. When the water in the pot reaches the boiling point, the steam, or water vapor, will hit the pan lid and the coolness caused by the ice should turn the vapor back into liquid form, or condensation. This represents what happens when clouds form. Eventually you will see water dripping off the pot lid and into the bowl. This represents precipitation.


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2 comments:

  1. Great great lessons! My oldest is taking chemistry this year. The word frightens me, I must admit, but chemistry labs can be so much fun!

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  2. Thanks for sharing at After School!

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