Chemical Changes

Let’s start out with this experiment. Take a film container (you know, those black little Tupperware containers that your film comes in when you buy it) and on the cap put a small piece of putty or anything sticky. Then, take an Alka-Seltzer tablet and stick it to the putty (you might have to break it in half to fit it on). After the cap is set, fill the bottom part about half-way with vinegar. When that is done place the cap back on securely and turn the whole film container over. What happens?

Now think about how the Alka-Seltzer and vinegar reacted with each other. What is left? Are the starting "ingredients" the same afterwards? Where have you seen this before?

If you need help on what it looks like follow this diagram.

Now here’s another brainteaser for you think about. Say you have a nail made of iron. Now you cut that piece in half. Is it still iron?

Take an identical nail made of iron and throw it into a blazing hot campfire. Assume that the campfire is so hot that the iron begins to melt. Is it still iron?

Again, take another nail made of iron and let it sit outside and rust. Is it still iron?

What is a chemical change and what makes it so different from a physical change? A chemical change is a change in matter that occurs on the molecular level. Many times, this change is irreversible, meaning you can’t go back after the change has been done. In the example with the iron nail, the first two changes are physical changes, because the end product is still iron. You cut it in half, it is still iron. You melt it, even though it is shaped differently, it is still iron. However, if the iron rusts you can’t take rust and make it into iron again. Therefore, the rusting of iron is a chemical change. It also turns out that you can change rust back into iron, but it takes so much energy that it almost never happens.

So what distinguishes a chemical change? Well, certain changes have tell-tale signs that identify it as a chemical change.

Color change: When iron becomes rust, it doesn’t have the same color anymore. It now has an reddish-brown color. Next time when you are drinking iced tea and you put lemon in it, take a note at the color. The iced tea becomes a shade lighter and that is because of a chemical change between the tea and lemon juices.

Gas evolution: No, not that kind of gas (which is technically called "flatus")! When there is a chemical change sometimes gas is released. This gas is the result of the chemical reaction and the chemical change. When you mix baking powder with vinegar a gas is let loose and it bubbles. That gas is the product of the baking soda and vinegar mixing.

Heat: Burning wood is a classic chemical change. When wood burns it becomes ash. When it burns it produces heat. This heat is just a product of wood burning and indicates a chemical change.

Light: Glow sticks are very common in showing that light is an indicator of a chemical change. Among other things, light from fireworks and light from lightning bugs is also a product from a chemical change.

So, going back to the experiment mentioned above. Is there a chemical change going on, and how do you know? If there is a chemical change, then how many indicators of a chemical change can you name?

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