Solubility Fireworks

Fill a tall bottle most of the way with water.

Place about a tablespoon of cooking oil in a cup.  Add a few drops of different colors of food coloring and stir them into the oil as best you can. (Limit yourself to one or two colors of food coloring - I used a bunch and it just ended up looking black - not what I was going for!)

Pour the oil onto the water in the bottle and observe.

There are a few lessons to be gleaned from this fun demonstration:
--Oil is less dense than water (i.e. it floats on the water)
--Food coloring is a polar substance, oil is non-polar (food coloring doesn't dissolve in the oil)
--Food coloring and water are both polar substances (food coloring dissolves in the water)

Sewer Bugs: Observation, Inference and Density

This demonstration is often used to catch students' attention.  You can use it as such, or turn it into an observation activity for your students.

In the classic set-up: 
Before your students arrive, you'll pour some Mountain Dew into a glass (another light colored soda would work as well, but there's just something about that neon yellow color of Mountain Dew... ) and add a handful of raisins.

The raisins should start traveling up and down in the soda.

When the students arrive, you show them your sewer bugs, making up a story about how you acquired them and so on.  At the end of the story, you drink the bugs (remember, you know it's just soda and raisins) - disgusting your students and forever imprinting yourself on their brains!

As a student activity: 
Provide your students with the supplies.  Let them set it up and observe carefully to see if they can determine how the "bugs" are traveling.

The explanation: 
Raisins have lots of nice bumps and creases to which the carbon dioxide bubbles (found in the soda) can adhere.  The carbon dioxide bubbles decrease the density of the raisin, allowing it to rise to the surface.  When the raisin reaches the surface of the soda, the bubbles pop.  The density of the raisin increases and it drops.  Carbon dioxide bubbles once again adhere to the raisin and the cycle continues.

How Does That Work: Doing the Back Float

This is a simple activity, but its explanatin is a bit sophisticated.  Therefore it's a good candidate for older and/or more advanced students.  But, don't let that stop you from trying it with younger students - keep your explanations basic and you might be surprised at what they take away from it.

What you'll need:

Baby oil

Water

Water bottle

Index card

Sharpened pencil

Hole punch

What to do:

Prepare a bottle, filled about half way with water and the remaining way with baby oil. 

On one side of an index card, color with a pencil, getting as much graphite as you can onto the index card.

Use a hole punch to punch the index card.

Place the hole punches into the bottle of oil and water.

What you'll see:
The dark side of the holes will always face the oil and not the water.  You can shake it up and they'll always return to that position.

Why:
Graphite is a good conductor, which gives it a negative polarity.  Water also has polarity, and it repels the graphite, so the graphite side will face the oil.


You can also talk about things like density, immiscibility and the like with this activity.

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How Does That Work is a series of products and demonstrations that you can present to your students and challenge them to explain the science of how they work. Make sure you decide ahead of time what you'll accept as a valid explanation - can it be printed straight off the internet, written in the student's own words, or does the student need to be able to explain it to you conversationally? What will a valid explanation earn the student - a prize, extra credit, a feeling of goodness?

Density: Float an Egg

What happen if you put an egg into a container of water? 

It sinks.

How can you make it float? 

You need to make the egg less dense or the water more dense.

I don't know how to readily change the density of an egg, but I do know how you can make the water more dense: SALT. 

Start adding salt a tablespoon at a time.  It takes a bunch of salt, so don't give up.  Eventually, there will be enough salt dissolved in the water and the egg will float. 

*****
A Note:
Don't be all fancy and use kosher salt.  Regular old salt works better - the smaller size makes it dissolve easier. Go ahead, ask me how I know (and then look at the picture above to find the answer).

How Does That Work: Frustration Bottles

There are so many things you can talk about with this demonstration: solubility, density, immiscibility, etc.  It also makes a good How Does That Work demonstration. 

In short:

You have three bottles, each made of two layers, but in one bottle the layers are reversed.  The bottles are filled with water (on the bottom) and baby oil (on the top).  In two of the bottles, the water is colored with water soluble food dye (which will color water but not oil).  In the third bottle, the oil is colored with liquid candle dye (which will color oil, but not water).

In long:

You'll need:

3 (500mL) water bottles

750 mL baby oil

750 mL water

food coloring

liquid candle dye

Fill 2 of the bottles with 250 mL of water.  Fill the remaining bottle with 250 mL of baby oil.

Use the candle dye to color the baby oil (do this before coloring the water - the water and food coloring are much more forgiving and easier to dispose of should you need to start over).

Use the food coloring to color the water, attempting to match the oil color as best you can.  Keep track of what you used and repeat with the second water bottle.

Into the bottle with the oil, add 250 mL of water.

Into the two bottles with water, add 250 mL of baby oil to each.  Cap.  (You may wish to run some glue along the cap so they are more resistant to being opened).

Leave the bottles on your front table/desk and let the students explore.  They'll try to turn the "wrong" one upside down.  They may try to shake them and then watch them separate.

Should lead to some good discussions!

You can keep these forever - put them in a safe spot until you need them the next time!

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How Does That Work is a series of products and demonstrations that you can present to your students and challenge them to explain the science of how they work. Make sure you decide ahead of time what you'll accept as a valid explanation - can it be printed straight off the internet, written in the student's own words, or does the student need to be able to explain it to you conversationally? What will a valid explanation earn the student - a prize, extra credit, a feeling of goodness?

Density: A Sweet Demonstration

Before your students arrive, unwrap a Snickers candy bar and a 3 Musketeers candy bar (any size is acceptable).

Have a large, transparent container filled with water set up in the front of the classroom.

Drop the two, seemingly identical, candy bars into the water.

One floats, one sinks.

Why?

Nuts are dense. The Snickers, packed with peanuts, sinks to the bottom, while the nut-less 3 Musketeers floats.

You could test your students’ understanding of density by asking them to predict what would happen with other size 3 Musketeers bars. For example, would a king size candy bar float or sink? Some might think it will sink because it’s bigger, but remember, density is an intrinsic property, it doesn’t depend upon size.

Density: Coke Cans

A classic…
Fill a small aquarium (or other clear container that can hold enough water) with water. Place a can of Coke and a can of Diet Coke in the water. The Diet Coke will float while the regular Coke sinks. Very little artificial sweetner is needed to sweeten the Diet Coke, as compared to the sugar used in regular Coke.

Some extensions…

Test your students understanding of density by using different sized cans of soda, if you can find them.


Measure out the amount of sugar and artificial sweetner used in each can to show students. Once you have it measured, store them in small plastic bags, so you have them for next time.