Mystery of the Red Cups

Introduction:

Successful science depends largely on our ability to make careful observations of the world around us. Demonstrations that highlight the importance of precise watching can be interesting and fun for kids. In this activity, we will  use one of the most unusual and amazing substances ever created to illustrate how observations play an critical role in the development of new knowledge and ideas.  As a silent demonstration, this activity promotes student-centered thought where students must independently observe, explain, and infer about the key ideas of the activity. For English as a Second Language Learners, this process can occur in their native language and so much of the learning is independent of their comprehension of the local spoken language.

National Science Standard: Unifying Concept

Nature is predictable and we can use evidence to explain and understand it.

Georgia Performance Standards:

Students will exhibit curiosity, honesty, openness and skepticism S(K-5)CS1

Describe materials, what they are made of, and how they change. SKP1, S2P1,S5P2

Materials: 

Safety goggles

Silent Teacher Led Exploration:  

We begin this exploration by playing the shell game using three cups instead of three shells. The cups need to be identical, opaque, and white on the inside. Place about 1/4th of teaspoon of Waterlock into two of the cups before students come into the class. Have the three cups placed out on a table for your students to see. 

Show the students that you are about to do a demonstration and you want them to observe it very carefully. Point a finger at your eyes and then your ears to help prepare them.  Show them that you are going to pour water into one of the cups and that their job is to follow the cup with the water in it as you scramble the cups around and around. Show them that the cups are empty by tipping them sideways in their direction (they will not be able to see the white powder). Pour about 1/4 cup of water into one of the cups that has the Waterlock in it and then scramble the cups around for a minute or so (the Waterlock will absorb the water and gel it in the bottom of the cup). After moving them around, point to each cup and have the students vote on the cup that they believe contains the water.  Students generally have no trouble following the correct cup.  Next, carefully invert the one empty cup to show them this  isn't the right one. Finally, invert the cup that they all voted on and watch their surprised reaction when no water flows from the cup.  Repeat this process using the second cup that contains Waterlock. 

Now show  the students that you want them to brainstorm  ideas to explain what happened to the water.  You may choose to have an index card that has "brainstorm" printed on it in the different languages that are spoken in your class.  Encourage them to think of as many ideas as possible by counting on your fingers to represent the new possibilities. This should all be done independently without any talking or discussion.

After a couple of minutes, go to the board and write "Explain" and then number 1-5 or so below it.  Raise your hand to demonstrate that you want them to share their ideas. Briefly write each idea that is offered on the board and praise them silently for their creativity.  Then, take out your container of Waterlock (sodium polyacrylate) and, using a teaspoon, let them carefully observe this substance. Next, place the spoon of this powder into a clear cup of water, mix it very quickly, and remove the spoon.  Allow the students to observe the Waterlock as it quickly absorbs the water. After a few seconds, you can invert the cup to show that the water will not pour out.  You can also tap the inverted cup on the table until the gelled water falls out. You can then pick it up like a snowball and show it to the rest of the class. Finally, redirect their attention back to the red cups and they will quickly recognize that there was Waterlock placed into two of the cups. Tap the two cups upside down on a table until the chunks of Waterlock fall out.

After students have seen the amazing ability of Waterlock to absorb water, have them predict different ways that this substance could be used.  You may again choose to have an index card that has "predict" or "predict uses" printed on it in the different languages the are spoken in your class.  After giving them a few minutes to think, write "Uses for Waterlock" on the board and list the ideas of your students.  Praise your student for their creative ideas and if they don't come up with the most popular use (diapers), start sucking your thumb and acting sleepy. When students suggest "babies" start patting on your behind and they will quickly figure out that diapers contain Waterlock in order to absorb the potty that babies so often produce. 

Class Discussion/Concept Building:  

This is a great silent demonstration because it is very counterintuitive and thus it is curiosity stimulating and thought provoking. It helps students to recognize the importance of making good observations and it allows them to see how substances can undergo amazing changes when combined together. Waterlock is a molecule that has an amazing ability to absorb up to 800 times it's own weight in water. That means that if you were a 100 pound chunk of this stuff and you jumped into a swimming pool, you would absorb over 80,000 pounds of water from the pool.  As a result Waterlock is used often in places where water and water-based spills are a problem. For example, Waterlock is used by plumbers to gel up the water from leaky pipes before it can soak in and cause major damage. But the most famous and profitable use of Waterlock is in diapers where it is sewn into the fabric so that the babies urine (mostly water) gels rather than leaking through the diaper and pants.  Since babies use between 3 to 4 thousand diapers before being potty-trained, Waterlock has proved to be a very useful and profitable invention.  

As a side note, substances, including water,  usually move from where is more crowded to where it is less crowded (from higher to lower concentrations). The water molecules move into the center of the sodium polyacrylate molecules because there is less water on the inside then there this on the outside.  This causes the water to "gel". You can reverse the process by adding sodium (table salt) to the glass and stirring it.  

Teacher Notes: Waterlock (sodium polyacrylate) can be purchased from www.teachersource.com

Safety Concerns:  Although Waterlock is not toxic, you should avoid letting students touch it because if crystals get from their fingers to their eyes it can be very irritating. Anyone who does touch the Waterlock should rinse their hands thoroughly after the demonstration.  You can dispose of it by washing it by throwing it away or washing it down the sink with a lot of water.

Extension: 

New uses for Waterlock are being developed every year. Have students brainstorm additional ways that Waterlock could be utilized to improve our communities. As a homework assignment or extra-class activity, have students determine how much water a disposable diaper can hold before it starts to drip. Have them slowly add water (distilled works best) one cup at a time and see how much the diaper can hold. It is amazing. You can color the water yellow if you want to and it should hold at least a liter of water.