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 4: Compound Chemistry


Crystals, polymers, pH and chemical reactions are all what happens when compounds of chemicals are formed.
Thunderegg, also known as spherulites, are radial crystals extending from the center. The minerals forming the crystals in Thundereggs could have come from hot water moving through cracks in the cooling lava rock, or later when mineralized groundwater oozed through. Either way, quartz and other minerals precipitated out of the water into the thunderegg cavity. The crystals began to grow.


Crystals

Crystal Snowflakes, 2010

Common Crystals


There are many common crystals around your house. Gather what you have available, such as Borax, Epsom Salts, Table Salt and Sugar. Have your students examine the crystals with a magnifying glass. If you use more than one type of crystal, compare them.

These are the Borax crystals.

To grow larger crystals from these small crystals, heat water to boiling in a saucepan. In small heatproof container pour 1/2-1 cup of water. Add about half the volume of the small crystals to the water, stirring until it dissolves. Continue adding small amounts of solid until the water is super-saturated, which means water has absorbed as much solid as it is able and the solid will no longer dissolve. If you want, you can add food coloring. You can pour this solution into small containers to allow the larger crystals to form. We used plastic eggs that you get around Easter time. Fill each eggshell with as much of the solution as it will hold without tipping or over-flowing. Place the shells in a safe dry place to allow the water to evaporate. As the water evaporates, crystals will form inside the eggs.
These are the table salt crystals.

These are the Epsom Salts crystals.

The one side of the Epsom salt "geode" made one very large crystal.

The rest of the Epsom salt crystals were like this.
Salt Lapbook, August, 2010
"Salt dissolves in water, and as the water evaporates the salt appears in beautiful crystals."- Handbook of Nature Study, p. 753

"Let each pupil take 5 tablespoons of water and add to this about 2 tablespoons of salt, stirring the mixture until it is dissolved. When the water will take no more salt, let each pupil...lay (a square of paper in the saucer, pressing it down beneath the surface...."
-HNS, p752

2008
"'Saturated solution' is an uninspiring term to one not chemically trained; and yet it merely means water which holds as much as it can take of the dissolved substance." -HNS, p753

It took about a week for us to notice salt crystals emerging on the black paper, creating an impression of a "starry night." The crystals are large because they look a long time in forming.

August, 2010
August 2010
We made crystals a second time. This time we kept one inside, which took about a week to appear. These crystals were smaller than our sample last time.The other set-up was put in a sunny spot outside which only took a few days for the water to evaporate, leaving large crystals behind. Look at how saturated this piece is!
Have you ever really looked closely at snowflakes? To make this easier, take piece of black construction paper and slip it into a plastic protector sleeve. Put this in the freezer to get it good and cold or the snowflakes will melt on contact. The black construction paper gives good contrast so you can see the snowflakes and the plastic sleeve keeps the snowflake from melting into the paper. You can see some flakes with the naked eye, but a magnifying glass reveals even more. If you look closely enough you can see that the flakes are in different shapes, such as hexagonal plates and stellar plates. What kind of observations can you make between the type of snow and the shape of the crystals?
Crystal Snowflakes, 2010

Comparing Crystals to Rocks

Gem Mining at Home
"The Alum that you buy has been crushed into a powder. In this experiment, you will reconstruct its natural form, which is crystalline. You will see how different the structure of a mineral is compared to a rock."
-Exploring Creation with General Science by Dr. Jay L. Wile


The Difference Between Rocks and Minerals
A string is suspended in a saturated solution of alum.
The Difference Between Rocks and Minerals
The weights are to keep the suspended into the solution.
This is left for from a few hours to a few days.
The Difference Between Rocks and Minerals

Scientific demonstrations don't always turn out the way you would expect. The importance is in the wondering and the discovery. After several days, as you can see, we had alum crystals "growing"on the string, but they were even larger on the side of the glass...perhaps there was something wrong with my string. Perhaps it was coated with something that prevented the crystals from collecting there. Despite this, we did get to see the alum crystals on the side of the glass.


"If you compare the alum crystals to rocks, you should notice a strong difference. Minerals make up most of what we find in the earth. Sometimes, the minerals can be found in their pure form. When that happens, the minerals usually have a sharp, geometric pattern. Most of the time, however, the minerals are not found in their pure form. Instead they are found in the form of rocks, which are usually made up of more than one kind of mineral."
-Exploring Creation with General Science by Dr. Jay L. Wile


The Effect of Temperature on the Solubility of Solid Solutes

For this experiment, you will need a canning jar (or beaker), 1/4 cup measuring cup, a stove, a candy thermometer, a coffee filter (or filter paper), a saucepan and a funnel.

Put 1/4 of salt and 1/4 cup of water in a saucepan. Set up your filtering system by putting a funnel in a canning jar or a glass measuring cup. Heat the salt-water mixture until it reaches 95 degrees F. Pour the solution into the filtering system until you a clear solution.  It should be clear because all undissolved salt should have been filtered out by the filter paper. This is a saturated solution of table salt.  Now place the solution in the freezer for about 20 minutes. Remove from the freezer and examine. There should be crystals of salt lying on the bottom of the canning jar. 
crystals in jar
source

What happened?
crystals on wood
source
The solubility of a solute depends on temperature. For solid solutes, the solubility increases with increasing temperature. In order for a solid to dissolve, the solvent molecules must be able to muscle in between the solute molecules and drive them away from each other. The heat provides the energy needed to make the solvent molecules more successful at muscling in between the solid molecules.

Rainbow Crystals, November 2009
Rainbow Crystals

The scientific name for these superabsorbant crystals is "cross-linked poyacrylamide copoymer gel."



Polymers



You can make your own polymer you can play with. Just mix together equal amounts of Elmer's white glue and Liquid Laundry StarchAdd food coloring as desired.
Sam (2008) with Elmer's white glue homemade Gak

This can be used like Silly Putty.
For another recipe, you can use Borax instead of the Liquid Laundry Starch. Make two bowls of mixtures.

Mixture 1:
1 ½ cups warm water
2 cups Elmer’s Glue
Food coloring

Mixture 2:
3 tsp. Borax
1 cup Warm Water

Make sure both are mixed well.
Pour mixture 1 into mixture 2. When it is in a glob work it for 2-3 minutes. Initially it feels wet but it eventually dries up to the final product.

Polymers are long chains of molecules hooked together. You can illustrate what is happening in the experiment by using 3 chains of paper clips laying side by side.
Show your students that the paper clip strands slide by each other easily, and this is how the glue alone acts. Then hook two from one chain to two from another chain, making cross-links.
Show your students how the chains cannot easily slide back in forth now, illustrating the changes that occur when the laundry starch is added to the glue.

The polymer of balloons are so tightly bound together you can actually stick a skewer into them and it won't pop the balloon because the polymer molecules wrap themselves around the skewer!


Acids and Bases

Acids and bases are another aspect to explore when you are looking at compounds. Acids donate hydrogen ions when they are mixed with other substances. (Remember that an ion is an atom that has lost or gained an electron.) A base accepts hydrogen ions.


Chemical Reactions

We have seen this demonstration of a chemical reaction in many places, but have never done it ourselves. We decided to hold our own experiment by comparing the reactions of Diet Coke with that of Diet Pepsi. We used five Mentos with a 2-liter bottle. I taped a 3-foot measuring stick to the bottle to give us an idea of height comparisons.
I actually could only get 4 Mentos in the Pepsi before it exploded on me.


As you can see, Diet Pepsi won out on our test by a landslide.

Why does this reaction happen with diet soda and Menthos?
It is caused by something called nucleation. Bubbles of carbon dioxide "nucleate" shortly after the pressure is released from a container of carbonated liquid. Nucleation often occurs more easily at a pre-existing "interface", or a surface forming a common boundary among two different phases such as using string to make crystals form rock candy from a sugar-water solution. The surface of the mint Mentos is such an interface, as it is covered with many small holes that increase the surface area available for reaction, thereby allowing CO2 bubbles to form with such a rapidity and in such a quantity that a geyser is formed. A 2006 episode of the television series MythBusters reported that when fruit-flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas mint-flavored Mentos (with no such coating) added to carbonated drink formed an energetic eruption.

There are lots of experiments that can demonstrate the difference between physical and chemical change.

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3 comments:

  1. There are so many great ways to see a reaction and chemical compounds in here. I LOVE it!

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  2. Wow! Thank you for taking the time to put this together. It's so comprehensive. I'm bookmarking it to be referred to many times I'm sure.

    ReplyDelete
  3. I am adding this to our must do science list. I appreciate the detailed post! Good stuff. Thank you for sharing.

    ReplyDelete

Thank you so much for taking the time to comment. It means so much.