Explosions

If there is one thing kids people love, it's explosions. And studying these kinds of reactions are an exciting way to explore chemistry.

I usually like to start small, with reactions kids may have seen before and that are safe for them to play with. Mixtures of baking soda and vinegar are a classic, but try swapping out the vinegar with other acids (lemon juice, for example). And if you have a thermometer, watch for the temperature drop as the reaction takes place. You can also do the reaction in a soda bottle, topped with a balloon, to show that carbon dioxide is generated during the reaction.

Another fun reaction is yeast and peroxide. Personally, I go for the easy packet of yeast directly into a cup of 3% peroxide from the grocery store. It yields lots of foamy fun. You can also make a solution of dry yeast in warm water, so that the little guys are awake and active before mixing, to see if that affects the reaction. My friend Elizabeth McCarthy from South Mountain Coop, also does the reaction with frozen peroxide and dry yeast. Because the reaction is exothermic (it generates heat), the reaction itself melts the peroxide and drives the reaction further.

One more classic reaction is Mentos and Coke. You can do a demonstration of a full roll of mint Mentos into a 2-liter bottle of diet Coke, which has considerable "Wow" factor, of course. But it's a great opportunity for scientific exploration as well. Give the kids several types of soda and candy, and have them work through various combinations. (There is a great Mythbusters episode on this reaction, which I encourage you to watch.)

Slightly more dangerous, and requiring a brief safety warning, are dry ice experiments. The sublimation process that allows the frozen carbon dioxide to go directly to gas is both scientifically interesting and fun to watch. It's important to note to students that, though we call this substance ice, it is not water at all, but rather a completely different material, created through pressure and deep freeze. After letting students observe pelleted dry ice for a while, add warm water and create some fog. Then add a bit of dish detergent -- the resultant bubbles filled with fog are very exciting and perfectly safe to touch. Later the foam will freeze into "snowballs" which are also fun for play, especially at the height of summer.

From there you can move into more dangerous reactions. One of my favorites is burning magnesium ribbon in a block of dry ice. Not only does this look really cool, but the resulting residue, a ribbon of white MgO covering a core of black carbon, is neat. Older students may enjoy discussing how you get this layered effect. (The chemistry behind this reaction is available online.) Be sure to remind students not to look directly at the light; it's extremely bright!

Then there is my favorite reaction, the most dangerous one I personally do: thermite. A mixture of powdered metal and a metal oxide, when heated the combination undergoes an exothermic oxidation-reduction reaction that sends sparks flying. And it is awesome. This is the stuff used in welding and fireworks. After everything cools, you can retrieve the blob of iron left behind as a fond memory of your favorite explosions.

Fun with dry ice

Let's face it, dry ice is fun. A super cold solid form of carbon dioxide, dry ice sublimates at room temperature, creating an eerie fog. Not only is dry ice great for science experiments, it's fun for parties too.

Luckily it's not that hard to get either. I have a local distributor called The Ice Factory, where I can drive right up and ask for a 30 lb. block any day of the week. You need to bring a cooler with you, or your frozen treasure won't last very long. A good pair of work gloves are needed to allow you to handle the stuff. I often ask to have it pelleted, for ease of use. But, as you'll see below, a big block of dry ice can be a lot of fun too.

So what do you do with your dry ice, once you've got it at home? I like to let kids explore the pellets alone first, observing the fog and talking about what's happening. Then we add warm water. The warmer the water, the more fog you get, because the difference in temperature affects the rate of sublimation. If you use a large clear container, kids can also see the bubbling as gas is generated. A little food coloring helps.

Then I like to add some dish soap. Suddenly everything changes, and big cloudy bubbles emerge from the container. Popping them releases the fog held inside. It's a ton of fun. Again add a bit of food coloring for added excitement.

Later, when all the dry ice is gone, the frothy, frozen soap will be left behind. It's lots of fun to play with too!

Remember how I said I like to get a big block of dry ice as well? If you use a power drill to add a wide hole to the top of the block and smaller ones to the sides, you can create a really amazing demonstration. You'll need magnesium ribbon as well.

Magnesium is a common alkaline earth metal. It's highly reactive and burns readily, producing a bright white light. Which is pretty cool all by itself, right?

When you place the magnesium ribbon in the dry ice and light it, things get dramatic. The burning magnesium can seal oxygen from the carbon dioxide in the dry ice, burning brightly without the need for other oxygen. In turn, the exothermic reaction speeds the sublimation of the dry ice, resulting in even more fog. The science is fun, but the visual is even better!

If you decide to try this at home, be sure to do it outdoors, or in a well ventilated area. And be sure to remove flammable items. This can get hot and bits of magnesium can be thrown off.