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West Chester Area School District, East Goshen Elementary School Keystone teacher Bill Turner took some digital photos of science in action and shared his class' experiences studying chemical reactions. Bill relates his tale of the investigation below. See Bill's class explore rockets too. Hot Yellow Yuck…and other neat stuff! One of our fifth grade units in science is called "Cooking with Science." In this unit we study matter and learn how it interacts. One of my favorite activities is studying chemical reactions. During my introduction to the first lesson in this series, we talk about ways to identify a chemical reaction. I teach my students that when a chemical reaction occurs, new matter is created. We can often tell that a chemical reaction has occurred because there is a color change, light or heat is given off, bubbles form, and the change is usually not reversible.
To illustrate a chemical reaction I have the students
measure and mix sodium bicarbonate and calcium chloride,
both of which are white solids, in a plastic baggie. Into a
small measuring cup I have the students pour a measured
amount of Phenol Red. They carefully place this cup in the
baggie as well.
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Phenol Red is a pH indicator and will turn yellow in the
presence of an acid or red in the presence of a base. Before
spilling the Phenol Red and starting the reaction, I ask the
students how we will know a chemical reaction has occurred.
I ask if there are ways to measure some of the anticipated
reaction. Someone invariably suggests using a thermometer to
measure the temperature so we add that as well.
Finally, the children seal the baggie and mix the chemicals.
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When the reaction has run its course, the two white
substances and the Phenol Red have mixed to form a yellow
substance inside the baggie. The baggie has filled with gas
and the thermometer registers a change in temperature. All
of these indicate that a chemical reaction has occurred and
hence the name: Hot Yellow Yuck.
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As a follow-up to the lesson and the activity, I have the
children work together in small groups to create poetry that
describes what has happened and what they have learned.
Since this activity has, in the past, coincided with Dr.
Seuess's birthday, that makes it a natural! To make matters
even more embarrassing, the students have to perform it in
front of the class!
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Our exploration into the wonders of chemistry does not stop
here, though. We also explore the world of polymers.
Polymers play an important part in our lives. We seem to
find them everywhere around us: plastics, nylon, polyester,
silk, wool, DNA (!), cellulose, and proteins, to name a few.
Polymers are large molecules that have special properties
because of their size and because the molecules become
entangled with one another. The word polymer comes from the
prefix "poly," which means many, and the word "mer," which
means part or segment. So a polymer is a material made of
many segments.
To learn more about polymers, I have my students mix two very common materials: Elmer's Glue and Borax (in solution). When these are mixed in the proper proportions, a substance very much like Silly Putty forms. Actually, when it is first formed, it is more like a slime then a putty. |
It has to be worked by kneading it between the student's
fingers and squeezing it with their hands. The children
always groan when I show them how to do this. Hmm…in
all the years I've done this activity, not one single child
has opted to NOT knead it with their fingers. Of course,
some have a little better luck than others!
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Another polymer is Sodium Polyacrelate, or Waterloc. This
substance is used in diapers. If you cut open a diaper
(preferably unused), it's the white powder that comes out.
This substance can absorb 100 times its weight in water.
That's why diapers work so well! I like to introduce this
activity by having three paper cups in front of me. I've put
a tiny amount of Sodium Polyacrelate on the bottom of the
third cup, just enough to cover the bottom. I tell my
students that we are going to use the power of thinking to
turn water into a solid. I get a cup full of water from the
sink and pour it into the first cup. We all do the "mind"
thing; everyone tries to "think" as hard as they can. I pour
the water into the second cup and tell them that they didn't
think hard enough. We try the "mind" thing again and I pour
the water into the third cup. Again, I admonish the class
for not thinking very well today and tell them that this is
their last chance. After they have REALLY struggled to make
thinking a visible, tangible activity, I turn the third cup
upside down and, of course, the polymer has turned the water
to a gel!
Each child is given a small quantity of Sodium Polyacrelate in a cup. They add water to it and observe how the water changes into a gel. |
This process is reversible just by adding salt. When the
students ask if they can touch it, I let them. After a
little contact with their fingers, the gel begins to turn
back into liquid again. Just the little salt in their sweat
is enough to reverse the process!
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