Watch Me Change!

Think about it!

You are much too smart to play with matches but let's pretend for a moment that you are going to light a match. Before you light the match you weigh it and find that it weighs two grams. You light it, let it burn, put out the flame, and weigh it again. What does it weigh? Choose one and then highlight the box below to find the correct answer.

A. Less than two grams?
B. Two grams?
C. More than two grams?

You're the scientist!

With the help of an adult, do the following activities: Remember to follow all of the safety rules and clean up your equipment when you have completed the activities.

Please read the instructions completely before beginning. Do not do these activities at your computer!

In the two previous activities, you measured the weight of things before and after a physical change. Did the weight stay the same? A physical change is a change where matter remains the same. It might change states, like from solid to liquid, or from solid to gaseous. Or, it might change shape or size, break into pieces, or dissolve or mix with another substance. But it is still made of the same kind of matter.

Do you think the weight of some things will stay the same if they go through a chemical change? A chemical change is a change where the chemicals in two or more different substances combine or change into a different kind of matter. One example of this is where vinegar and baking soda are mixed. There is a chemical reaction and the mixture begins to bubble and give off a gas. Do you think the weight of the new substances is the same as the weight of the original substances? Let's see if you can find out.

Making gas

In this activity, you will make gas by combining vinegar and baking soda.

Materials:

• Small plastic soda bottle - cleaned and dry
• Balloon
• Scale or balance
• Measuring containers
• Vinegar
• Baking soda

Procedure:

1. Weigh the plastic bottle. Record the weight.
2. Blow up the balloon a few times to stretch it out. Weigh the balloon and record the weight.
3. Measure 20 grams of baking soda and place it into the container.
4. Measure 20 ml of vinegar and place it in the plastic bottle. (20 ml of vinegar should weigh 20 grams, but you may want to make sure by weighing the vinegar).
5. Add the baking soda to the vinegar, quickly place the balloon over the bottle so that it is sealed.
6. Record your observations.
7. When the chemical change is finished, look at the product in the bottle. Does it look like vinegar and baking soda any more? What has happened to the balloon?
8. Weigh the bottle-balloon apparatus. Do you think this will weigh more, less, or the same as the reactants you started with?
9. Repeat the entire procedure except do not put a balloon on the bottle. You will add the weight of the bottle, the vinegar, and the baking soda this time. When the chemical change is complete, do you think the bottle will weigh more, less or the same as the original reactants?
10. Clean up your experiment.
11. In your notebook or using a computer, write a summary of the results of your lab.
12. Discuss the results of your experiments with the class.