Polymers: Glue + Liquid Starch

I've been playing with around with recipes to make assorted slimes and such in preparation for a library program this summer.

A simple slime to concoct uses glue and liquid starch (you can find it in the laundry aisle)

You can find people using all different proportions, but I use about equal amounts of each (I eyeball it) poured into a cup.  You can add food coloring to the mixture as you desire.  Stir until things gel up (if it's too sticky, add more starch).  Then you can knead it with your hands.  (You can rinse off any extra starch).  As you play with it, it will become more smooth and gel/putty like.

You might also want to try using clear glue , with or without food coloring for a different effect.

Conservation of Matter: Steel Wool & Vinegar

This is another versatile demonstration to use in your student of chemistry - learn about chemical changes, chemical reactions, conservation of matter and even air pressure.

Depending upon the take-home message you want your students to get, you might structure the activity in a few different ways, but the basics are the same.

You'll need some steel wool, vinegar, bottles or flasks and a balloon.

Pull apart some strands of steel wool and push some into each bottle.  Pour some vinegar onto the steel wool.  (Some instructions tell you to soak the steel wool in the vinegar for a few minutes and then remove the steel wool.  I just left mine in it).

Stretch a balloon over the opening of one bottle, but leave the other as is.

You could find the mass of each system at this point, if you're interested in conservation of matter.

Allow the bottles to sit and the reaction to occur. 

The vinegar removes the coating from the steel wool, and the steel will be begin to oxidize in the presence of oxygen. 

As the reaction is occurring, the balloon will be pushed into the bottle.  Why?

The oxidation reaction is using up the oxygen in the bottle, which will lesson the number of air molecules in the bottle, thus reducing the pressure in the bottle.  Because the pressure outside the bottle is greater than the pressure inside the bottle, it will push the balloon in. 

You can stop there if you're interested in simply looking for evidence of a chemical change, studying the chemical reaction or seeing the affects of air pressure. 

If you're interested in conservation of matter, continue on. 

Find the mass of each system once again.

The closed system (i.e. the one with the balloon covering the opening), should have the same mass it had in the beginning. 

The open system's mass should have gained mass, as it continued to pull more oxygen into the system to carry out the reaction further. 

The Ivory Soap "Explosion"

I absolutely love it when I learn a new science trick.  At this point, I've seen quite a few, and while there are always new-and-improved versions out there, it's not too common for me to come across something brand new.  Which is one of the reasons I love this demonstration (and it's just SO cool).  It's apparently a well-known demonstration, but I've missed it up 'til now.  (And that's another reason why I make a point of sharing the "classic" science experiments that so many have already seen - everyone has to learn about them for the first time, some time). 

On with the demonstration....

Begin with a bar of Ivory soap (or you may want to use a sliver of soap.... you'll see what I mean). 

Make the appropriate observations of the soap. 

Place the soap on a microwave-safe plate. 

Make a hypothesis* about what will happen when the soap is heated in the microwave.

Now heat the soap in the microwave - set the time for 2 minutes, but keep an eye on it (you'll be doing that any way, trust me).

Observe the soap carefullly.

The soap will expand to a huge volume.  If you use whole bar of soap, it will nearly fill the microwave!  Great wow factor! 



It deflated a little at this point, because my camera's batteries died at this point and I had to wait for them to recharge.



Why does this happen....

Remember when the Ivory floated because it had more air in it than the "other" soap?  When the Ivory is heated, the soap softens and the air bubbles expand.

How can you use this in your science class?

1. A follow-up to the previously mentioned density experiment.
2. A discussion of gas laws (Charles Law, specifically) - when a gas is heated, its volume will increase. 
3. A lesson on physical and chemical changes.  Explosions are chemical changes by definition.  This demonstration looks like explosion, but it's not.  It's just a physical change. 

*A funny story - I told my 5 year old that we were going to do a science experiment after dinner.  He asked what we were going to do and all I would tell him is that we were using soap.  Then I asked if he had any hypotheses about what would happen to the soap (knowing absolutely nothing about what we were going to do to it) and he said "It's going to explode."  I think he was a little surprised at how close to right he was!

End of School: Playing with Polymers

Tracy from The Science Spot has come through once again with a fantastic unit, Playing with Polymers, in which students make four different polymers - Gloop, Boogers, Goobers, and Super Slime.

Tracy does this as part of curriculum, as part of a study on petrochemicals.  I did it at the end of the school year, and the one drawback to doing it then is that this activity does require quite a few supplies and pieces of equipment.  But, the students LOVE it - I'll take the mess if I can have engaged students right up until school's out! 

And, Tracy does make it fairly painless for the teacher; she includes lists of materials (in quantities for 100 students), recipes, set-up instructions and so on.  If you keep the materials well-organized and labeled, things will go smoothly.  And your students will love you!

States of Matter: From Solid and Liquid to Gas

This is a very simple demonstration, good for very young students who are just beginning to grasp the differences between solids, liquids and gases.  It's also a fun demonstration of chemical changes for older students.  I mean really, who doesn't love a good baking soda and vinegar reaction?!?

Put some baking soda into a balloon (you might want a funnel to do this).  You might want to put some on a plate as well, so the students can observe it. 

Pour some vinegar into a bottle.  You might want to allow the students to watch you pour, so they can see how the vinegar flows and takes the shape of the bottle. 

Place the balloon over the bottle, being careful not to dump the baking soda in at this point. 

Lift up the balloon, so the solid pours into the liquid.

In a matter of moments, you'll have captured the third state of matter: a gas (carbon dioxide).

Homemade Indicator Papers

If you've made some cabbage juice indicator and are looking for another way to save it for longer use, try making your own indicator papers.

Cut paper (I used coffee filters) into strips about 1/2" wide and a 2-3" long.

Submerge the strips in cabbage juice until they are fully soaked.

Remove the strips and place them in a warm spot to dry.

Store the dried strips in a resealable bag.

To use, place a drop of the liquid to be tested on the paper.  If it's a base, it will turn pink.  If it's a base, it will turn green.  And if it's neutral, there will be no color change.

The color change isn't as drastic as you'd see with litmus paper, but it's there. 

Cabbage Juice Indicator

Red cabbage juice is a great indicator - it turns pink in an acid, green in a base, and stays blue in a neutral substance.  And while it takes a little time to make, it's a whole lot cheaper than other indicators. 

To make some: 
Chop up a head of red cabbage and place it in a large pan.  Cover the cabbage with water.  Simmer for about 20 minutes (your house will smell like cabbage).

Let the contents cool before you remove the cabbage.  Store the water (now cabbage juice) in a jar*.

To test your cabbage juice:
Set up three glasses:
Pour a little vinegar in the first, some baking soda dissolved in water in the second, and tap water in the third.

Add a few drops of cabbage juice to each glass and observe.

*You can freeze the cabbage juice for longer storage.  Pour it into ice cube trays and freeze.  Then place the cubes in a freezer bag or box.  Pull out individual cubes as you need them.

Chemical Changes: Gak

Prep Work:
Create a solution of Borax in water. Pour a small amount of the solution in small cups (one for each student or pair of students).

Dilute some white glue with water, 1:1.  Put a small amount of the diluted glue in small cups (one for each student or pair of students).

Activity:
I use this as an introduction to chemical changes, so students don’t really have any background information.

Provide each student/pair of students with a cup of the Borax solution. They should document any observations they can make.

Provide each student/pair of students with a cup of glue. They should document any observations they can make.

Ask students to predict what will result if the contents of the two cups are combined.

Pour the Borax solution into the glue cup.

Stir the mixture using a stirring rod, popsicle stick, or straw.

After stirring, pour the excess water into the sink.

Knead the gak with your hands for several minutes until it is no longer sticky.

Document any observations that can be made about the putty.

Discuss the ways in which properties of the gak differ from those of the initial substances.

**Borax should be no where near student's mouth or eyes.  Wear safety glasses and wash your hands thoroughly after doing this activity.  If you can't trust your students not to drink the Borax solution, don't do this activity.

Chemical Changes: Pennies, Salt & Vinegar

Dissolve some salt in a small amount of vinegar.

Hold one penny half way in the solution.  When you pull it out, you'll see this...

The part that was submerged in the solution is shiny copper.  The portion that remained out of the solution remains dull with copper oxide tarnish (dark brown and/or green).

Now put 20 pennies in the solution and let them sit for about 5 minutes.

Remove the pennies and...
Rinse 10 of the pennies off and let them dry.
Just let the other 10 pennies dry.

Rinsed pennies are on the left.

Now wait an hour or so....

(Rinsed pennies are now on top)

So, What Happened?

The vinegar/salt solution removed the copper oxide from the pennies, leaving a clean copper surface on each penny.

Over time, all of the pennies will become tarnished with copper oxide once again, as the copper reacts with oxygen in the air.

The vinegar/salt solution that remains on the pennies that were not rinsed speeds up the oxidation process, so in an hour you're left with pennies that look like this:

******
Presented at the 2003 New Jersey Science Convention.

Volcanoes: Make a Model

You can find all sorts of volcano making/exploding kits to buy.  (If you're interested in buying, each of those words is a link to a different product).

But you can save your money and have a little more (messy) fun by making your own.

Start with an empty bottle - a Snapple bottle or soda bottle works well.  Tape it to a paper plate - makes it sturdier and easier to work with.

Mix up some paper mache.  There are all kinds of recipes out there.  I'm partial to just flour and water - cheap, easy to procure, and easy to clean up.

Dip strips of torn up newspaper in the paper mache and start applying them to the bottle.  Build up the shape of the volcano as you wish.  Make sure you keep the top of the bottle open!

By making your own model, you have the chance to make it the shape you want... make it a shield volcano, a cinder cone volcano, a composite volcano.  Even if you don't have a sepcific plan, it gives you a chance to review and discuss those types of volcanoes and how they're formed.

A cinder cone volcano

Allow your volcano to dry - the amount of time this takes depends on the weather and how heavy-handed you were with the paper mache.

Once the volcano is dry, you can choose to paint it. 

Or you can just get on with the exploding part.

Put some baking soda in the bttle.  You can add some red food coloring, for effect, if you wish.  Pour in some vinegar and stand back and watch!

And, if you're too impatient to build the volcano and just want to get to the exploding part, you can just put some baking soda in an empty bottle, add some vinegar and watch.  It's a good demonstration of a chemical change, even if you aren't studying volcanoes!

Chemical Changes: Clean Your Silver

Line a non-metal container with aluminum foil.

Place tarnished silver in – make sure it touches the aluminum foil.

Boil water and add baking soda (1T per cup of water).

Pour this solution over the silver.

You'll quickly discover some shiny silver and may see a yellow haze on the aluminum foil.

I didn't fully submerge the lid, so you can see some of the tarnish at the top, and the "polished" part at the bottom.  It's not the best photograph, but it is nice and shiny (so much so that it reflects all kinds of other stuff and ruins my picture). 

Why:

The tarnish is silver sulfide, which forms from a reaction with sulfur in the air.   Sulfur has a greater affinity for aluminum than it does for silver.  So when you place the tarnished silver in the baking soda solution, the solution carries the sulfur to the aluminum.  The yellow haze on the foil is the sulfur that has been deposited there. 

The chemical equation:
Silver sulfide + Aluminum --> Silver + Aluminum Sulfide

Some Side Notes:
After hearing about this demonstration numerous times, I decided to give it a try (and get some pictures so I could share it with you).  It worked so well!  The yellow that's left on the foil isn't real apparent, although you could see an outline from where things had been sitting.  But, what was very apparent was the smell of sulfur, as soon as the solution was poured over the silver.  Wow!  I wasn't expecting that, but it certainly confirmed that the tarnish was composed of sulfur!  I'm now in search of a large enough vat to use to "polish" the teapot that goes with this lid! 

One more thing.... when researching the exact chemical equation I learned something else.... traditional silver polishes actually remove small amounts of silver along with the tarnish.  This method only removes the tarnish.  Seems like the way to go - no polishing and keeps the silver fully in tact!
*****
Presented at the 2003 New Jersey Science Convention.