Chemical Changes
4th Grade
Daniel F. Fink, Lashonda Orrell and Lila Levendoski
References: (Checked 1/2005)
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2003-04 Columbus Public Schools Science SLC Guide
http://www.wow.osu.edu
Benchmarks:
SLC 11: Identify the characteristics of a simple physical change.
Objectives:
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Students will identify a chemical change as the formation of a new substance and
describe signs that a chemical change is occurring [e.g. burning, rotting fruit,
digestion, evolution of a gas].
They will identify a physical change as a change in size, shape, or state of matter.
Students will distinguish between a physical and a chemical change.
Materials:
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Baking Soda
Rusty Nail
Vinegar
Book of Matches
Clear Plastic Cups
Piece of Raw Potato
Safety Goggles
Hydrogen Peroxide
Apple [Macintosh if available] – cut in half
Borax
Banana – peal and split open
water
Elemer’s glue
Plastic bags
Initial Demonstration:
Ask the students what happened last week when we put the tablets into the
canisters. [The tops blew off]. Why might that have happened? [A gas was made]
Where did the gas come from? [It came from a reaction between the water and the tablet].
Ask the students if they can think of any other examples of a chemical change.
Target Observations:
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When you mix an Alka-seltzer tablet with water in a closed container the lid
blows off.
Target Model:
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Sometimes when you mix substances together, a new substance is made- this is a
chemical reaction.
Procedure: [It is suggested that you pick 1-3 of these activities/demonstration depending
upon how much time you have to spend and the level of ability of the students]
Put on safety goggles!
1. Pour baking soda into a clear plastic cup so that the bottom of the cup is just
covered. Slowly add vinegar to the cup to fill it about halfway and observe the
formation of carbon dioxide gas, an indication that a chemical change has taken
place.
2. Place a piece (about the size of large eraser) of raw potato in a clear plastic cup.
Add enough hydrogen peroxide to cover the piece of potato and observe the
formation of oxygen gas as the enzymes from the food break the peroxide into
water and oxygen gas. The gas formation is an indication that a chemical reaction
is taking place. The kids can also feel the outside of the container – it will be cold
to touch. This is another indication of a chemical reaction.
3. Combine half of a cup of warm water with about a teaspoon of powdered laundry
detergent and stir to dissolve. Make a small amount of Epsom salt solution by
dissolving 1 part magnesium sulfate in two parts water. Add a drop of food
coloring to the Epsom salt solution, and then use an eyedropper to add a few
drops of the colored solution to the laundry detergent solution. As a clear
indication of a chemical reaction, a solid will immediately form and settle to the
bottom of the cup. These solutions may already be prepared and labeled for use. If
so, fill the cup about one fourth of the way with the detergent solution and pour in
a few milliliters of the Epsom salt solution to observe the formation of the solid.
4. Take the apple and the banana and cut them open. Show the class the white color
of the fruit. Set aside and show the class the difference in color towards the end
of the period. The turning brown is a result of oxidation. This is a chemical
change similar to rusting metal where oxygen in the air is reacting with the fruit
tissue to make a new [and icky!] substance.
5. Flubber/Gluep Mix a 1:1:1 ratio of Borax, water, and glue. It is recommended
that you put the borax in a half-filled film canister. Pass out a second film
canister with a half-full mark on it. Have the students dump the borax into a
plastic Ziplock bag [do not chintzy!!! Get a good kind!!!]. Then have the
student’s fill the marked canister up to the half-full line with glue [for practice
measuring], and pour it into the bag. Then fill the canister to the half-full line
with water and pour that into the bag. Have the students mix the chemicals by
squeezing the bag.
When a new substance is made, that is a chemical change. How can you tell if a
chemical change is occurring? You can look for a new substance [a solid precipitate, rust
on the outside of a nail, browning of fruit] or sense other changes such as bubbles
[indicates the formation of a gas] or a new smell [think of garbage and the
browning/rotting apple/banana] or a change in temperature [the flubber/oobleck] that
might indicate that a chemical change is occurring.
Target Observations:
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Mixing vinegar and baking soda made a bubbly mess. There was a lot of fizzing
The potato experiment made the container cold. There seemed to be some kind of
gas coming out of the potato.
Something solid formed in the Epsom salt solution, something that was not there
before.
The longer the fruit sat out, the more brown and yucky it became.
The flubber stuff was not at all like the ingredients we used to make it.
Target Revised Model:
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When a chemical change occurs you will be able to observe the formation of a
new substance.
Sometimes you will be able to see that a material is new b/c of a change in color,
smell, or b/c you will see bubbles or smoke.
Other times that you will be able to observe a phenomena that allows you to infer
that a chemical change has occurred.
Procedure:
Tell the students that now they are going to try and differentiate between physical
and chemical changes.
Take a match, and rip it out of the matchbook, ask if this was chemical or physical
change. Light the match and ask again.
Take the fruit again, cut it, and ask [physical]. Point to the part that has been
sitting out all class period and ask [chemical].
Target Observations:
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The match made a smell, as well as flame. The cardboard/wood part of it looks
burnt.
The fruit had a different shape and size, but was still fruit.
The exposed part of the fruit was brown and icky looking. The fruit still looked
fresh where it had just been cut.
Target Revised Model:
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Sometimes it is hard to tell if something is a chemical or physical change b/c
sometimes the happening at the same time.
Remind students to identify a chemical change as the formation of a new
substance and describe signs that a chemical change is occurring [e.g. burning,
rotting fruit, digestion, evolution of a gas].
Remind students to identify a physical change as a change in size, shape, or state
of matter.
By looking for these traits students will be able to distinguish between a physical
and a chemical change.
Summary:
Students should be familiar with the differences between chemical and physical
changes. The students have been exposed to a variety of chemical reactions, all of which
produced new substances. Each of the mini-experiments gave off wildly different clues
to indicate a chemical reaction- the students should be more adept at picking these out,
and inferring that a chemical change has occurred.