Anna Cajiga
SME 301
Matter Summary
January 27, 2005
Title
Using Alka-Seltzer to Demonstrate the Law of Conservation of Matter
Benchmark
Area: Physical Science
Category: Changes in Matter
Benchmark: Describe common chemical changes in terms of properties of reactants and product.
(Middle School)
Misconception
Disregard for conservation of particles during a chemical change.
Background
There is a common disregard for conservation of particles during a chemical change.
However, this experiment explores what actually happens when a chemical change takes place.
A chemical change is one in which the original substance or substances becomes a new
substance or substances after the change is complete. Putting Alka-Seltzer into water is a
chemical change because the reaction of these two substances creates a new type of matter – a
gas. After this, and any, chemical change, the number of atoms in the substance will still be the
same as it was before the change.
Materials
Balance
Measuring Cups
Two Empty Water Bottles (16 oz.)
Two Balloons
Eight Alka-Seltzer Tablets
Four Cups of Water
Directions
1. Make sure that the balance is balanced. Each side should be level with the other side.
2. Fill each water bottle with two cups of water.
3. Put a water bottle filled with water, a balloon and four tablets of Alka-Seltzer on each side of
the balance to ensure that each set of materials weighs the same before the chemical change takes
place.
4. Remove the materials from the right side of the balance. Carefully break these four AlkaSeltzer tablets into pieces small enough to fit through the mouth of the balloon. Be careful not to
lose any pieces. Place all of the pieces inside of the balloon.
5. Attach the balloon to the water bottle by stretching the opening of the balloon over the top of
the bottle. Be careful not to let the Alka-Seltzer tablets fall into the water.
6. Replace the water bottle (now with the balloon attached to it) on the right side of the balance.
Lift the balloon so the Alka-Seltzer tablets fall into the water in the water bottle.
7. Wait a few minutes and draw a picture of what you see happening.
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Results
At the conclusion of this experiment, the balloon attached to the water bottle appears to
be filling up and “growing”, just like if you were to blow up a balloon with your mouth.
Although though the balloon on the right is being filled, the balance remains even and balanced.
Discussion
Through this experiment, it becomes clear that when a chemical change occurs, mass is
conserved. Since each side of the balance is equal, the mass is the same for the substances that
went through a chemical change and the substances that did not go through a chemical change.
This proves that all of the atoms in the original substances are still present after the chemical
change has taken place. The reason that atoms are neither lost nor gained during chemical
changes is because during this type of change the bonds between the atoms of the original
substances are breaking apart and new bonds are being formed with different atoms. When the
atoms form these new bonds, they are creating different types of molecules, which in turn make a
different type of matter or substance. This is why after a chemical change, the original
substances have changed to different substances. This also explains the Law of Conservation of
Matter, which states that matter only changes form during physical and chemical changes, but is
never created or destroyed. This experiment demonstrates the Law of Conservation of Matter
because when the chemical change occurred in this closed system, all of the atoms were
conserved and the mass remained the same.
Matter is conserved also during physical changes. During a physical change the
molecules of the substance remain the same, but they are rearranged and this causes changes in
physical properties or appearance. An example of physical change is when matter changes state,
like when water changes from solid (ice) to liquid. Matter can be found in one of the three
physical states – solid, liquid, or gas. In any of these physical states, the molecules that make up
matter are always the same, they are just rearranged differently and moving at different speeds.
Matter can change states when heat is added or removed from it. There are six types of state
changes in matter. When matter changes from solid to liquid, heat has been added to the matter
and the change is called melting. Adding heat can also change matter from liquid to gas, and this
is called evaporation. A gas can change into liquid when heat is removed from it. This change is
called condensation. Removing heat from a liquid can change it into a solid. When this occurs, it
is called solidification. A solid can change into a gas when heat is added to it, this process is
called sublimation. Removing heat from a gas can turn it into a solid, and this is called
deposition. The energy from heat causes the molecules in matter to move and hit each other.
When matter has little energy from heat, its molecules move slowly and hit each other with little
force, and therefore come closer together, this happens in a solid. When heat is added to the
matter, its molecules move faster and hit each other harder, moving farther apart from each other.
If enough heat energy is added to a solid, its molecules will move apart farther until it turns into
a liquid. If even more heat is added, the molecules will have more energy so they will move
faster and hit each other harder. With enough heat, the molecules of a liquid will travel fast
enough and far enough to turn it into a gas.
Sometimes, heat is added or taken away from matter, but not enough heat energy for a
change of state to occur. However, this does not mean that the movement and arrangement of the
molecules remains the same. If heat is added to matter, the molecules that make it up begin to
move faster. As they move faster, they bounce harder against each other, which causes them to
spread further apart. Since the molecules are further apart after heat is added, the matter is now
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taking up more space. This is called thermal expansion. The opposite happens when heat is taken
away from matter. The molecules that make up matter begin to move slower, which means they
are hitting each other with less force. Since there is less force driving the molecules away from
each other, they move closer together, making the matter take up less space. This is called
thermal contraction. It is almost as if thermal expansion and contraction are one step away from
a complete change of state because enough heat is added or subtracted to increase or decrease the
motion of the molecules, but not enough to completely change the arrangement of the molecules
into a different state. There is one exception to thermal contraction and expansion. This
exception is water. When water freezes, the molecules move closer together and form a lattice
that has empty space in the middle. This makes the frozen water take up more space than the
liquid water. Similarly, when ice cubes melt, the lattices that were formed break apart and the
liquid water takes up less space than the frozen water did.
We can see evidence of these concepts in our everyday lives. For example, on a cold
winter day when you go outside, you can see your breath in the air. This is because when the
cold air touches the moisture from your breath, the molecules begin to move slower and that
moisture condenses, making tiny particles of water that we can see. The same sort of thing
happens when you take a can of soda out of the fridge and set it on the table. The moisture in the
air touches the cold can, causing the molecules in this moisture to move slower and closer
together. As a result, the moisture in the air condenses into water on the sides of the soda can.
Learning about changes of state also allows us to explain why candle wax melts when we light
the candle. The heat from the flame warms the wax and the molecules in this solid begin to move
faster and spread further apart. This causes the wax to change to a liquid. Understanding thermal
expansion and contraction also allows us to explain many everyday occurrences. These concepts
explain how a thermometer works. When a thermometer is placed in a cup of hot water, more
heat is added to the mercury inside the thermometer and the molecules that make it up begin to
move faster, hit each other with more force, and spread apart. This makes the mercury take up
more space and move further up the scale on the thermometer so we can read the correct
temperature. When we remove heat by taking the thermometer out of the hot water, the
molecules in the mercury have less heat energy and they begin to move slower, hitting each other
with less force. This makes them move closer together, and therefore the mercury takes up less
space. We can also understand why it is easier to remove a tight metal lid on a jar if we place it
under hot water. Heat is transferred from the hot water to the metal lid, and the molecules move
faster, hit each other with more force, and spread further apart. This causes the metal lid to
expand and makes it loser on the jar. If we did not know that water is the exception to thermal
expansion and contraction, we would not understand why a plastic water bottle bursts when we
fill it and put it in the freezer. Because the molecules of water form a lattice with empty space in
the middle when it changes from a liquid to a solid, the water takes up more space when it is
frozen and causes the water bottle to burst. Chemical changes occur all around us, and knowing
more about chemical changes helps us to identify and understand them. Every time you eat a
meal, thanks to chemical changes, the food becomes substances your body can use, such as
vitamins or sugars. The substances in our body interact with the substances in the food we eat,
and the atoms of the food are rearranged into new substances that our bodies can use for
nourishment. We all know that our bodies cannot digest rice or beans when they are raw. We can
change them chemically through cooking so that we can digest them normally. This is because
the act of cooking the rice or beans creates a chemical change and the atoms of these substances
rearrange to form new substances that our digestive system can deal with. We can now also
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understand how stain removers work. If you get a grass stain on your favorite pair of jeans, a
stain remover will get rid of it because the substances in the stain remover interact with the stain
to cause a chemical change. The stain remover will break apart the atoms in the grass stain so
that they can be washed away in the washing machine.
Classroom Resources
1. Experimenting with Physical and Chemical Changes
Written by Gordon R. Gore
This book is helpful because it presents readers with several hands-on experiments that further
explore and explain important concepts relating to matter and, more specifically, physical and
chemical changes in matter.
2. Bill Nye the Science Guy Video – Episode #8 Phases of Matter
This episode of Bill Nye the Science Guy is a great classroom resource because it uses
demonstrations and detailed explanations to teach viewers what molecules are and what happens
to them as matter changes from solid to liquid to gas, all in an attention-grabbing and humorous
way.
3. Field trip to Impression V Science Center in Lansing, Michigan for the Slime! Lab
This field trip is useful because it allows visitors to experience hands-on learning about atoms,
molecules, states of matter and chemical changes when they become “real” scientists and mix
various chemicals together to create a new substance – Slime!
Credits
I developed this experiment on my own based an experiment my science class did when I
was in fifth grade. In this experiment, we put Alka-Seltzer tablets in film canisters and then
watched the lid of the film canister shoot off high into the sky. This experiment was intended to
show the pressure that built up as a result of the gas that was created by the chemical change. I
decided to modify this experiment to instead show that when a chemical change takes place, the
atoms do not disappear but instead simply rearrange themselves.