Diet Coke and Mentos

Materials: One 2-liter bottle of Diet Coke, one roll of Mentos, two sheets of paper

Diet Coke and Mentos are two things that just about everyone has consumed at one time or another. But did you know that they react violently when you add them together? Well, they do. You'll want to do this experiment outside in a grassy area.

To start with, roll one piece of paper up into a tube that's just a little bit wider than the mouth of the Coke bottle. This will be used to deliver the Mentos. The other piece will be held underneath this tube, so that you can pull it out quickly and all the Mentos will drop into the bottle at once.

Now open your bottle of Diet Coke (other sodas will work, but Diet Coke gives the best reaction in our experience). Place one sheet of paper over the opening, and hold the tube directly over the opening. Pour the Mentos into the tube, pull out the sheet of paper (allowing the Mentos to drop into the bottle), and step back! You should see a fountain of Diet Coke foam erupt from the bottle.

Why does this happen? Well, there are two reasons. Diet Coke, as you know, is carbonated - that means that it has carbon dioxide (CO₂) dissolved in it. This CO₂ would much rather be a gas than be dissolved in a liquid, but it has no way of coming out of solution. Until, that is, you add the Mentos. Mentos have a very rough surface, which means that they have a large surface area. All these surfaces give the CO₂ plenty of places to form bubbles. The second reason that the CO₂ can come out of solution so fast has to do with surface tension. Normally, the bubbles of CO₂ would have a difficult time breaking the surface of the Coke. When the Mentos dissolve, however, the sugars that go into the liquid lower its surface tension, and the bubbles will be able to break the surface, resulting in a geyser.

Interestingly, similarly-textured candies (like Altoids) don't work very well for this experiment. That's because they're not dense enough. The Mentos are heavy enough to drop to the bottom of the Coke, helping all the CO₂ along the way nucleate into bubbles. The Altoids, which are less dense, only affect the CO₂ at the top of the bottle. So, no geyser. Use Mentos to get the full effect of this one.

"Kick-the-Can" Ice Cream

Materials:

This is a fun and easy way to make some ice cream. In the small can or tupperware container, combine the milk, cream, sugar and vanilla. Do not fill the can more than half full or the ice cream will not freeze as well. Cover the small can with a plastic lid and place it into the bucket. Fill the bottom half of the space between the two containers with ice and add the rock salt. Fill the rest of the space with ice and put on the plastic lid. You may want to tape the lids on both containers, just in case.

Now you get to roll or kick the bucket around for about ten minutes. Go crazy, but don't let the lids come off!

After ten minutes, remove the lids and scrape the ice cream from the sides of the small can. Stir the mixture. If the ice cream needs to freeze longer, pour the saltwater out of the bucket. Set the small can back into the bucket, along with more ice and rock salt as needed.

When the ice cream is ready, there will be about half an inch of frozen mixture on the sides of the can, with the rest still in near-liquid form. Scrape the frozen ice cream off the walls and stir it into the liquid ice cream to create the right consistency. This recipe makes about 2 cups. You can add frozen fruit to the mixture if you like; it will also freeze a bitt faster that way.

Enjoy!

Do-it-Yourself Volcano

Materials: Empty 2-L soda bottle, baking soda, vinegar, liquid detergent, red food coloring

Unfortunately, hot lava is hard (and dangerous!) to make in your house. But you can still make a volcano! Here's how.

First, get an empty soda bottle (maybe the one from the Mentos experiment!) and pour in 2 tablespoons of baking soda (sodium bicarbonate, NaHCO₃), a few drops of the red food coloring, and 6 drops of the liqid detergent. Fill the bottle about 2/3 of the way up with some warm water, stirring or shaking to make sure the baking soda dissolves. Now slowly pour in some vinegar (acetic acid, CH₃COOH) and stand back! You may want to do this experiment outside, or at least in the sink.

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Slime!

Materials: Elmer's white glue (not the "washable" kind), Borax, ziplox bags, spoon, mixing bowl, large jar or cup, water

In the bowl, thoroughly mix an equal quantity of the Elmer's glue and water. In the jar or cup, combine a tablespoon of borax powder with a cup or so of water and stir. If all of the borax powder dissolves, then you need to add a bit more. When you get to the point where no more borax will dissolve, then the solution is saturated.

Now, add 2 tablespoons of the borax solution to the bowl with the glue and water mixture and stir quickly. The resulting mixture should be slimy or gooey. You can save your slime for a long time by putting the 'stuff' into sealable plastic bags. If your slime dries out, you can add a bit of water back into it. If it gets too dry, you'll have to start over.

When you mix the Elmer's glue and water, you make a substance (polyvinyl acetate) that is known as a polymer. The borax solution (sodium tetraborate) is a "cross-linking" substance that binds the polymer chains together, which make the polyvinyl acetate thicker. As the polymer chains get more cross-linked, it gets harder for them to move around, and the slime starts to get thicker. You can try adding more borax solution to see if this indeed makes the slime thicker or thinner.

Make Water Denser

Materials : Fresh egg, jug, water, salt.

 

Although ice and water are really the same molecule (H₂O), they are in two different phases and have two different densities; that's why ice will float in water. This property of ice is what keeps the ocean and lakes from being frozen and it also shields the marine animals from the cold. Here is an experiment to show you how it is possible to increase the density of water and thereby increase the amount of weight that it can float.

If you place a fresh egg in a jug of clean water, the egg will sink to the bottom. This is because the egg is much denser that the water. If we want to float the egg, the water has to become more dense. You can do this by taking the egg out of the water and adding some salt to the jug of water (about a cupful of salt to half a pint of water). Now put the egg back in the water - it floats!. If you try to place a block of ice into this salt water, you will notice that more of the ice shows above the brine than when it floated in fresh water. By adding the salt, you have significantly increased the density of the water, and therefore increased the amount of weight that can float in it.

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Propelling A Toy Boat

Materials: Card, scissors, pencil, large bowl, water, detergent or soap.

 

Did you ever wonder how it is possible that a water spider stays afloat on the surface of a pond? The answer is something called surface tension, which is related to how much force it takes to break the water's surface. A small bug doesn't have enough weight to move the water molecules apart, and so he can actually stand on the water's surface!

This experiment will show you how to make use of the surface tension of water not just to float a toy boat, but to make it move. First draw a simple boat on a piece of card, like the one shown in the figure. Make sure you use the right dimensions (2.25" to 1") so that your boat is the right size. Cut your boat out carefully, and don't forget to cut out the little triangle as well.

Fill a large bowl with water and place the boat in it to make sure it floats well. Now take a little detergent powder or a small piece of soap and drop it carefully into the small triangular opening in the stern of your boat. Within a few seconds, the boat will be traveling forward through the water. If your boat is cut evenly, it will travel forward in a straight line.

The boat is propelled forward as the detergent breaks down the surface tension of the water and tries to expand through the narrow opening in the rear of the model, creating a force on the toy boat. Try repeating this experiment with a drop of oil from an oil can or a small piece of camphor. They both change the surface tension of the water.

Questions:

Invisible Ink

Materials: Pen with clean tip, drawing paper, candle, vinegar or lemon juice.

Pour a little vinegar or lemon juice into a cup. Use a pen with a new tip or thoroughly clean the old tip so that no trace of ink remains on it. If you don't have a clean pen, you can even use a sharpened matchstick to write with. Dip the pen into the cup and write your message in large letters on the sheet of drawing paper. When the ink dries, the message will be invisible.

To make the message reappear, hold the drawing paper close to the flame of a candle or facing a fire; the message will gradually show as faint brown scorching. This is because the portion of the paper which absorbed the vinegar or lemon juice combines with oxygen from the air more easily than the untreated area of the paper. The process involved really employs oxidization of the vinegar or the lemon juice.

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Capillary Filtering

Materials: Two bowls, water, knitting wool or flannel strips, earth.

This experiment uses a wick (which you can make from a thin strip of flannel or several strands of knitting wool woven to form a thin rope) to filter suspended matter from water. To begin, stir some earth into a bowl of water. The particles will remain suspended in the water and discolor it. How are you ever going to separate the mixture?

Here's how to filter the mixture to get clean water free of earth again. Raise the bowl of muddy water onto a box or pile of books. Suspend your wick over one side so that it hangs down into a lower bowl. Capillary action will draw the water from the top bowl down into the lower bowl and after some time you will see droplets of clear water falling from the free end of the wick.

The same arrangement can be used to make sure your favorite plant receives regular watering when you are away. Place a bowl of water on box above you plant and run a thread of wool from the water to the earth of your plant. While you are away, water will flow slowly along the wool and down into the plant pot, keeping the earth moistened and your plant healthy.

Rust Uses Up Oxygen

Materials: Steel wool, pencil, rubber band, water glass, dish of water.

Burning and breathing are not the only means of consuming oxygen. The chemical reaction which makes iron rust also uses up oxygen in the process. We can show this by a simple experiment.

Place the steel wool onto the tip of the pencil and moisten it with water. Secure it with a rubber band. Fill the dish with water and set up the pencil and steel wool inside the upturned glass. Place the dish and its contents in a safe place and leave it for several days. After some time, you will find that the steel wool has begun to rust and the water level in the upturned glass has risen. The rusting process used up oxygen form the air in the glass and the outer air forced up the level of water inside the glass to offset the area of low pressure created in the glass. When all oxygen has been used, the water will have risen to about one-fifth of the volume of the water glass. Do you know why?

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