FIREPROOF BALLOONS

Balloons are rather fragile things. You know that they must be kept away from sharp objects. The also need to be kept away from flames. A fire can weaken the rubber and cause it to burst. However, in this experiment you will find out how you can hold a balloon directly in a flame without breaking the balloon.

For this experiment you will need:

• two round balloons, not inflated
• several matches
• water

Inflate one of the balloons and tie it closed. Place 60 milliliters (¼ cup) of water in the other balloon, and then inflate it and tie it shut.

Light a match and hold it under the first balloon. Allow the flame to touch the balloon. What happens? The balloon breaks, perhaps even before the flame touches it.

Light another match. Hold it directly under the water in the second balloon. Allow the flame to touch the balloon. What happens with this balloon? The balloon doesn't break. You may even see a black patch of soot form on the outside of the balloon above the flame.

Why does the balloon with no water break in the flame? The flame heats whatever is placed in it. It heats the rubber of both balloons. The rubber of the balloon without water becomes so hot, that it becomes too weak to resist the pressure of the air inside the balloon.

How does the balloon with water in it resist breaking in the flame? When water inside the balloon is placed in the flame, the water absorbs most of the heat from the flame. Then, the rubber of the balloon does not become very hot. Because the rubber does not become hot, it does not weaken, and the balloon does not break.

Water is a particularly good absorber of heat. It takes a lot of heat to change the temperature of water. It takes ten times as much heat to raise the temperature of 1 gram of water by 1C than it does to raise the temperature of 1 gram of iron by the same amount. This is why it takes so long to bring a teakettle of water to the boil. On the other hand, when water cools, it releases a great deal of heat. This is why areas near oceans or other large bodies of water do not get as cold in winter as areas at the same latitude further inland.

EGG IN A BOTTLE

Here's an amazing way to get a hard-boiled egg into a bottle, even though the mouth of the bottle is smaller than the egg! What's more, you don't even need to touch the egg to get it to go in!
For this experiment you will need:
    • a hard-boiled egg
    • a glass bottle with a mouth just slightly smaller than the egg (a fruit-drink bottle works well)
    • a 8-cm by 8-cm (3-inch by 3-inch) piece of newspaper
    • a match
Remove the shell from the egg. Set the egg on the mouth of the bottle to see that the egg does not fit through the mouth.
Fold the piece of newspaper into a strip that can be dropped into the bottle, about 1 cm by 8 cm.
Light the match and use it to ignite the folded strip of paper. Remove the egg from the mouth of the bottle and drop the burning strip of paper into the bottle. Before the fire goes out, set the egg back onto the mouth of the bottle. Within a few seconds the egg will squeeze through the mouth and into the bottle.
As it entered the bottle, the egg may have broken into pieces. This happens when the diameter of the egg is more than about 0.5 cm (about 3/16 inch) larger than the diameter of the bottle's opening. A medium or small egg may be small enough to enter the bottle without breaking. Also, rubbing some cooking oil onto the mouth of the bottle will make it easier for the egg to slide into the bottle without breaking.
A similar effect can be produced using a water-filled balloon in place of an egg. Just pour water into a round balloon to fill it without stretching it, then tie it shut. When the filled balloon is the size of an egg, it can be used in the same way as the hard-boiled egg.
Why does the egg slide into the bottle, even though no one is pushing it? Because the pressure of the air is pushing it. Before the burning paper was put into the bottle, the pressure of the air inside the bottle was the same as outside the bottle. The burning paper, however, heats the air inside the bottle. This causes the air inside to expand. When the egg is placed on top of the bottle, it seals the bottle, and the fire eventually goes out. When the fire goes out, the air inside the bottle cools. As it cools, the air contracts, and the pressure of the air inside the bottle becomes less than the pressure outside. Then, the higher outside pressure pushes the egg into the bottle!

FIZZING AND FOAMING

With just a few household chemicals you can turn a glass of colored liquid into a froth that overflows its container.

For this experiment you will need:

• 15 cm³ (1 tablespoon) of baking soda (sodium bicarbonate)
• 15 cm³ (1 tablespoon) of laundry detergent
• about 180 milliliters (3/4 cup) of water
• about 60 milliliters (1/4 cup) of vinegar
• several drops of food coloring (optional)
• a 400-milliliter (12-ounce) drinking glass
• a waterproof (plastic or metal) tray
• a teaspoon

Place the drinking glass on the tray. Put 15 cm³ baking soda and 15 cm³  laundry detergent to the glass. Add 180 mL of water and a few drops of optional food coloring. Gently stir the mixture to mix the contents of the glass. To display and observe the fizzing and foaming, quickly pour the vinegar into the glass. The mixture will foam up and over the top of the glass, covering the tray with a froth of tiny bubbles.

To produce a color change when the vinegar is added to the mixture in the glass, you can substitute some red cabbage juice for the optional food coloring. The experiment titled "Exploring Acids and Bases with Red Cabbage" gives instructions on how to prepare some red cabbage juice. With red cabbage juice, the mixture will chage color from blue-green before adding vinegar to red-orange after the vinegar is added. For a different color change, try grape juice.

In this experiment, the fizz is produced by a chemical reaction between baking soda and vinegar. Baking soda and vinegar react, and one of the products of the reaction is carbon dioxide gas. This gas forms bubbles that are surrounded by the liquid. The laundry detergent makes the bubbles last longer, and a foam is produced. The volume of the gas produced and trapped in the foam is much greater than the glass can hold, so some of it spills over the top of the glass.

Baking soda is sodium bicarbonate. Vinegar contains acetic acid dissolved in water. Sodium barcarbonate reacts with most acids. The products of the reaction with vinegar are carbon dioxide gas, sodium acetate, and water.

The reaction of sodium bicarbonate to form carbon dioxide gas is the basis of its use as a levening agent in baking. Cakes are solid foams. The foam is produced when bubbles of carbon dioxide from the reaction of sodium bicarbonate are trapped in the batter. As the cake bakes, the batter dries, and the trapped bubbles of carbon dioxide form the holes in the cake.

RUBBER BANDS AND HEAT

Just about everyone has used rubber bands, but few people have taken the time to observe the less obvious properties of these everyday objects. In this activity you will examine the thermal properties of rubber, that is, the behavior of rubber as it relates to heat, a form of energy.

In the first experiment you will attempt to detect heat flow into or out of a rubber band. To do this, you need a rather sensitive heat detector. Fortunately, you have such a detector with you at all times. Surely, you've felt the heat of a flame or the cold of an ice cube. Therefore, you know that your skin is sensitive to heat flow. In this experiment, you will detect heat flow using some of your most sensitive skin, that on your forehead or on your lips.

1. Place your thumbs through the heavy rubber band, one on each end. Without stretching the band, hold it to your forehead or lip. Does the band feel cool or warm or about the same as your skin? Repeat the test several times until you are sure of the result.
2. Move the rubber band slightly away from your face, so it is not touching your skin. Quickly stretch the band about as far as you can and, holding it in the stretched position, touch it again to your forehead or lip. Does it feel warmer or cooler or about the same as it did when it was relaxed?
3. Move the stretched rubber band away from you face. Quickly let it relax to its original size and again hold it to your skin. Does it feel warm or cool?
4. Repeat the stretching and testing, and relaxing and testing several times until you are sure of the results.

An object feels cool or cold to you when heat flows from your skin to the object. Conversely, an object feels warm or hot when heat flows from the object into your skin. If the stretched rubber band feels cool, then it absorbs heat from your skin. If it feels warm, then it gives off heat to your skin. If the band feels neither warm nor cool, then there is no detectable heat flow. These three cases can be represented as follows:

Case 1.		Relaxed Band + Heat Stretched Band
Case 2.		Relaxed Band Stretched Band + Heat
Case 3.		Relaxed Band Stretched Band (No Heat)

Which of these three cases best describes what you observed?

There is another way to test which of the three statements is correct. We can see what happens to the length of a rubber band if we heat or cool it.

1. Hang one end of the rubber band from the wall or ceiling and suspend a weight from the other end of the rubber band. (What you use for a weight will depend on what is available. The weight should be heavy enough to stretch the rubber band, but not so heavy that it is likely to break the band. For example, hang the band over a door knob and suspend a hammer from the band.)
2. Heat the rubber band with a hair dryer. Start the dryer and, when it has warmed up, turn its heat on the stretched rubber band. Does the stretched rubber band become longer or shorter when it is heated?

Does this observation agree with what you found in the first part of the experiment? Doing an experiment several ways and checking for agreement in the results is an important strategy in science.

When rubber is heated it behaves differently than most familiar materials. Most materials expand when they are heated. Consider the liquid in a thermometer. The thermometer works because the liquid expands when its temperature increases. Similarly, a wire made of metal, such as copper, becomes longer as it gets hotter. The expansion of metals with increasing temperature is the principle behind the functioning of home thermostats and of jumping discs.

Whether a material expands or contracts when it is heated can be ascribed to a property of the material called its entropy. The entropy of a material is a measure of the orderliness of the molecules that make up the material. When the molecules are arranged in an ordered fashion, the entropy of the material is low. When the molecules are in a disordered arrangement, the entropy is high. (An ordered arrangement can be thought of as coins in a wrapper, while a disordered one as coins in a tray.) When a material is heated, its entropy increases because the orderliness of its molecules decreases. This occurs because as a material is heated, its molecules move about more energetically. In materials made up of small, compact molecules, e.g., the liquid in a thermometer, as the molecules move about more, they push their neighboring molecules away. Rubber, on the other hand, contains very large, threadlike molecules. When rubber is heated, the sections of the molecules move about more vigorously. In order for one part of the molecule to move more vigorously as it is heated, it must pull its neighboring parts closer. To visualize this, think of a molecule of the stretched rubber band as a piece of string laid out straight on a table. Heating the stretched rubber band causes segments of the molecules to move more vigorously, which can be represented by wiggling the middle of the string back and forth. As the middle of the string moves, the ends of the string get closer together. In a similar fashion, the molecules of rubber become shorter as the rubber is heated, causing the stretched rubber band to contract

RAINBOW IN A GLASS

You will need the following materials:

• four different colors of food coloring (e.g. red, yellow, green, blue)
• five tall glasses or clear plastic cups
• ¾ cup (180 g) of granulated sugar
• a tablespoon for measuring
• 1 cup (240 ml) water

In the first glass, add one tablespoon (15 g) of sugar. In the second glass, add two tablespoons of sugar, three in the third glass, and four in the last glass. Then add three tablespoons (45 ml) of water to each glass, and stir until the sugar is dissolved. If the sugar in any of the glasses will not dissolve, add one more tablespoon (15 ml) of water to all of the glasses, and stir again. When the sugar is completely dissolved, add two or three drops of red food coloring to the first glass, yellow to the second, green to the third, and blue to the last glass.

In the remaining glass we will create our rainbow. Fill the glass about a fourth of the way with the blue sugar solution. Next, carefully add the green solution to the glass. Do this by putting a spoon in the glass, just above the level of the blue solution. Slowly pour the green solution into the spoon, raising the spoon to keep it just above the level of the liquid, until the glass is half full. Add the yellow solution, and then the red one in the same manner. What do you notice about the colored solutions?

The amount of sugar dissolved in a liquid affects its density. The blue solution has the most sugar dissolved in it and is therefore the densest. The other solutions are less dense than the blue solution, so they float on top of it. The densities of the solutions should be very close however, and the solutions are miscible, so you will see that the layers do not form well defined boundaries as in the first experiment. If done carefully enough, the colors should stay relatively separate from each other. What do you think will happen if you stir up the liquids in the glass?

LAYERED LIQUIDS

Have you ever heard the phrase "oil and water don’t mix"? First we will test that expression, then look at interesting combinations of several other liquids.
Oil and Water
You will need the following materials:
• ¼ cup (60 ml) water
• ¼ cup (60 ml) vegetable oil
• a small glass
• food coloring
First pour the water into the glass. Add a couple of drops of food coloring and mix. Next add the oil. What do you see? Which layer is on top?

Tightly cover the glass with plastic wrap or your hand (if it's big enough). While holding the glass over a sink (in case you spill), shake the glass so that the two liquids are thoroughly mixed. Set the glass down and watch what happens. Do oil and water mix?

The word “miscibility” describes how well two substances mix. Oil and water are said to be “immiscible,” because they do not mix. The oil layer is on top of the water because of the difference in density of the two liquids. The density of a substance is the ratio of its mass (weight) to its volume. The oil is less dense than the water and so is on top.

The next experiment examines the miscibility and density of several liquids.

Layered Liquids

You will need the following materials:

• ¼ cup (60 ml) dark corn syrup or honey
• ¼ cup (60 ml) dishwashing liquid
• ¼ cup (60 ml) water
• ¼ cup (60 ml) vegetable oil
• ¼ cup (60 ml) rubbing alcohol
• a tall 12 ounce (350 ml) glass or clear plastic cup
• two other cups for mixing
• food coloring

Take the 12 ounce glass. Being careful not get syrup on the side of the glass; pour the syrup into the middle of the glass. Pour enough syrup in to fill the glass 1/6 of the way.

After you have added the syrup or honey, tip the glass slightly and pour an equal amount of the dishwashing liquid slowly down the side of the glass. Does the dishwashing liquid float on top of the syrup or sink to the bottom?

Next mix a few drops of food coloring with water in one of the mixing cups. Color the rubbing alcohol a different color in another mixing cup.

Be careful to add the next liquids VERY SLOWLY. They are less viscous (i.e., not as thick) and mix more easily than the previous liquids. We don't want them to mix. Tip the glass slightly, and pouring slowly down the side of the glass, add first the colored water, then the vegetable oil, and finally the colored rubbing alcohol.

On a piece of paper, make a sketch of the glass and its liquids, labeling the position of each liquid in your glass.

Why do the liquids stay separated? Can you think of several ways that the liquids in the glass are different? Try to describe some properties that differ in each of the liquids in the glass.

One property that is different in all of the liquids is color. Another property unique to each liquid is thickness (viscosity).

The property of the liquids that is responsible for the layering effect is density. Can you guess what the relationship is between the density of a liquid and its position in the glass?

Another property that keeps the liquids separate is that some of them are immiscible liquids, in other words they do not mix with each other. As you proved in the first experiment, oil and water are immiscible liquids. On the other hand, water and rubbing alcohol are miscible and will mix with each other. Water and the dishwashing liquid will also mix.

Stir up the liquids in the glass and watch what happens to the layers. Have any of the layers mixed (are they miscible in each other)? Wait a few minutes and look again. Have any of the other liquids separated?