I have received so many comments requesting the "Where did the water go?" lesson from this post, that I decided to go ahead and publish it. I have to give credit to my fabulous coworker, Jennifer Crumpton, who shared this lesson with me. We do this lesson every year on the first day of school, and it does a fantastic job of getting students excited about science. I thought it would be nice to post it now because you have to get together some materials that most of us probably don't have on hand.
Where Did the Water Go?
This lesson is more of a demonstration than an actual science lab that students participate in. You will put 3 small paper cups in front of the students. You will pour water into one of the cups and then mix the cups up (like they do at sporting events where you have to guess which cup has the ball under it). The students will guess which cup has the water in it. You will "test" the cup by turning it over on a student's head. Your kiddos will be amazed when no water comes out of any of the cups!
Ahead of time you need to order some sodium polyacrylate (the stuff they put in disposable diapers to absorb liquid). You can order it here. You will want to practice this demo once or twice before you do it in front of your students.
Get three small paper cups (make sure you can't see through them). Before the students arrive, put a heaping teaspoon of the sodium polyacrylate into one of the cups.
What You Do:
1) At the beginning of the lesson, use a graduated cylinder to pour 50ml of water into the cup that you already put the sodium polyacrylate in. (If you don't have a graduated cylinder, you can just pour the water until a gel forms in the bottom of the cup. Using the graduated cylinder is a good way to show students how important it is to be exact when measuring during science labs).
2) Tell the students to keep their eye on the cup you poured the water in while you mix up the three cups. Keep moving the cups around until you think the students have gotten the cups confused.
3) Next, ask the students to guess which cup has the water in it.
4) Once they have chosen a cup, ask them how you can test whether the cup has water in it. Tell them you're going to test the cup by turning it over on a student's head! Randomly choose a student (you don't want your little friends thinking you have favorites!)
5) Walk up to a student and turn the cup over on their head. The kids will go crazy!
6) Do the same thing with the next two cups.
7) Once students realize that no water came out of any of the cups, have them write up a lab report. This is a great way to introduce the scientific method on the first day. Here's what I have them write in their science notebooks:
Question: Where did the water go?
Hypothesis: (They write what they think happened and why they think it happened). They can also share their hypotheses with their groups and with the class.
Observations: (They write down everything they saw me do.)
(Have students discuss what they think happened again. Then tell them your secret and write the conclusion together as a class.)
Conclusion: The water was absorbed by a polymer called sodium polyacrylate. The polyacrylate used in this activity is found in disposable diapers.
If you have the funds, you can purchase enough sodium polyacrylate to send some home in a baggie for each of your students. Make sure they know not to try and sniff or taste it!! They will enjoy performing this trick for their families, and it will answer the question of "What did you do at school today?" If you try this lesson, let me know how it goes!
Here is a blog post from Educational Innovations that has a variation of this lesson as well as some other lesson ideas for using sodium polyacrylate. Have fun!