Variables: an Alka Seltzer Experiment
Fifth grade Chemistry lesson
Liaison:
Date: 2/25/97
Group Members: Greg Sawicki and Karine Gibbs
School: Agassiz
Teacher: Mrs. Berger
Materials:
cups
alka-seltzer tablets
hot pot
water
ice
small beakers
balloons
Procedure:
The class is currently working with the kit "Variables" so we decided to go over what we had learned about experiments and apply the concept of variables to their knowledge of the scientific method. The kids already knew the parts of the experiment: question, hypothesis, observation, data, conclusion. We began by trying to define the word "variable." We asked what it sounds like, and some kids said "variety" and "vary" so from that we came up with a working definition of "things that you can change."
We then explained the experiment. Each group of 4-5 kids gets a beaker, water, balloon, and alka-seltzer tablet. They have to put water in the beaker, then put in the tablet and cover the hole with the balloon. They need to wait about 15 seconds and then measure (with a ruler) how big the balloon has gotten.
You can talk about what is in alka-seltzer that makes it give off carbon dioxide at this point, or you can wait till the end. From this, we made a list of the different variables in the experiment, and came up with amount of water, temperature of water, number of tablets used, and time waiting before measuring. We also established a control situation at 75 ml of water, one tablet, room temperature water, and 15 seconds of waiting time.
Each group then tested one variable at a time. It is important to stress that only one thing can be changed at a time. One group did the control, one had hot water, one had cold, etc.. Each time they got a new result they put it onto a class data table we set up on the board.
Each group tested about 3 different conditions, and then we came together to discuss the results. We made three graphs from the data: temperature vs. size showing an increase in size as temp. increases; # of tablets vs. size which showed a larger balloon with more tablers, and time waited versus size which showed increase with more time. We explained how graphs are important ways of taking data and making conclusions, and asked each kid to write down the graphs in their notebooks and write down the conclusions from the graphs.
We also explained the results in terms of molecules since the class had learned about molecules earlier. With higher temperatures, there is more space between the molecules, so more stuff can dissolve and more gas is given off. The other conclusions are pretty self-explanatory.
Evaluation:
This lesson is a good way to teach the scientific method and especially emphasize the role of variables in an experiment. The experiment itself is simple and not too messy, and the kids enjoyed coming up with their own conditions to test. Make sure to synthesize all the data as a group so the class can see what each of their classmates was doing!
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