Observations of Chemical
Changes
Hands-On Labs
Version 42-0182-00-03
Review the safety materials and wear goggles when
working with chemicals. Read the entire exercise
before you begin. Take time to organize the materials
you will need and set aside a safe work space in which
to complete the exercise.
Experiment Summary:
You will perform a variety of chemical reactions and
make scientific observations to describe the chemical
change. You will also investigate the results of heating
an object and burning an object.
EXPERIMENT
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Learning Objectives
Upon completion of this laboratory, you will be able to:
● Define chemical change and physical change, and identify similarities and differences.
● Identify the relationship between a chemical change and a chemical reaction, and describe
reactants and products.
● Define observable indications of a chemical reaction.
● Define a scientific observation and differentiate between an observation and a conclusion.
● Perform a series of chemical reactions.
● Make scientific observations and use them to make scientific conclusions.
● Distinguish between heating and burning and demonstrate each.
Time Allocation: 2.5 hours (including 30 minute waiting time)
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Experiment Observations of Chemical Changes
Materials
Student Supplied Materials
Quantity Item Description
1 Aluminum pie pan
1 Bottle of distilled water
1 Dish soap
1 Matches or lighter
1 Pair of scissors
1 Pair of sunglasses
1 Roll of paper towels
1 Sheet of black paper (or black tablecloth)
1 Sheet of white paper
1 Source of tap water
1 Sunlight (bright sunlight needed for 30 min.)
10 Toothpicks
HOL Supplied Materials
Quantity Item Description
1 Aluminum cup, 2 oz
1 Burner fuel
1 Metal tweezers
2 Pairs of gloves
1 Pair of safety goggles
1 Short stem pipet
1 Spatula
1 Test tube clamp
1 Test tube cleaning brush
4 Test tubes, 13 x 100 mm
1 Test tube rack, 6 x 13 mm
2 Well plate – 24
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Experiment Observations of Chemical Changes
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Experiment Observations of Chemical Changes
1 Experiment Bag: Observations of Chemical and Physical Changes
1 – Ammonium hydroxide, 1 M – 1 mL
1 – Copper (ll) carbonate in vial, ½ full
1 – Copper (ll) nitrate crystals in vial
1 – Copper (ll) sulfate, 0.2 M – 2 mL in pipet
1 – Hydrochloric acid, 1.0 M – 1 mL
1 – Lead (ll) nitrate, 0.2 M in pipet
1 – Magnesium metal pieces – 8-10 pieces
1 – Phenolphthalein solution 1% – 1 mL in pipet
1 – Potassium iodide, 0.1 M – 2 mL in pipet
1 – Silver nitrate, 0.1 M – 2 mL in dropper bottle
1 – Sodium bicarbonate, 1 M – 2 mL in pipet
1 – Sodium hydroxide, 1 M – 1 mL in pipet
1 – Starch solution, 1% stabilized – 2 mL in pipet 1 – Zinc, mossy
– 6-8 pieces, bag 2” x 3”
Note: Your bag MAY contain sodium hypochlorite rather than IKI indicator.
1. A computer to upload digital camera images.
2. Basic photo editing software, such as Microsoft Word® or PowerPoint®, to add labels, leader
lines, or text to digital photos.
3. Subject-specific textbook or appropriate reference resources from lecture content or other
suggested resources.
Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed
above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.
1 IKI indicator, 1 mL, 2.1 % in glass vial
Note: To fully and accurately complete all lab exercises, you will need access to:
Background
Chemical and Physical Changes
The terms “chemical change” and “physical change” are often used in chemistry, sometimes even
in the same sentence. However, chemical changes and physical changes are distinct from one
another. A physical change is a change in the form of a substance (appearance or state of matter),
while a chemical change creates a new chemical substance. Examples of physical changes include:
cutting an apple into pieces, mashing a banana, crushing a soda can, melting ice, boiling water,
or condensing vapor. In contrast, examples of chemical changes include silver tarnishing, an egg
cooking, burning a sheet of paper, or mixing baking soda and vinegar together to create a bubbling,
fizzing volcano. See Figure 1. A chemical change may also be referred to as a chemical reaction,
a process where the atoms of chemical compounds (substances) interact with one another,
rearranging to form new chemical compounds (substances).
Figure 1. Physical and chemical changes. A. Mashing a banana changes the shape and
consistency of the banana, but it is still a banana. © Kacso Sandor B. Crushing a can changes the
shape of a can, but it is still a can. © deisgn56 C. Tarnished silver, a new substance (silver sulfide)
is formed through the chemical reaction between silver and chemicals in the air, such as sulfur.
Note that the inside of the container is not tarnished as it was not in contact with the air. ©
Louella938
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Experiment Observations of Chemical Changes
Chemical Reactions
A chemical equation is the written representation of a chemical reaction, showing the relationship
between the molecules of the reactants (the starting chemicals) and the products (the new
chemicals produced through the reaction). In a chemical equation, the reactants are listed to the
left, and the products are listed on the right. Chemical equations are balanced, so that there are
equal numbers of each element on both sides of the equation. In the case of multiple reactants
or products, each is separated by a “plus” symbol. The reactants and the products are separated
by a reaction arrow.
For example, in the chemical reaction between potassium hydroxide and iron nitrate shown below,
the reactants are potassium hydroxide (KOH) and iron(III) nitrate (Fe(NO3)3), and the products are
iron(III) hydroxide (Fe(OH)
3
) and potassium nitrate (KNO
3
).
When read aloud, this equation states that “potassium hydroxide plus iron(III) nitrate yields
iron(III) hydroxide and potassium nitrate.” As chemical changes occur on a molecular level, it can
be challenging to determine if a chemical reaction did or did not occur. However, a series of physical
observations of a possible reaction between reactants can be used to help determine if a chemical
change has occurred. Observable indications of a chemical reaction include:
● Change in color
● Change in odor
● Formation of light
● Change in temperature (endothermic or exothermic)
● Formation of a solid (precipitate)
● Formation of gas (appearance of gaseous bubbles)
A light-creating chemical reaction
occurs inside of a firefly. In the abdomen
of a firefly, a chemical named luciferin
forms a complex with luciferase, ATP, and
magnesium, which then reacts with oxygen
to release light and return to the starting
materials.
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Experiment Observations of Chemical Changes
Making Observations
Observing and recording details is crucial in both making scientific observations and drawing
correct scientific conclusions. For instance, a product should be described as “yellow-orange with
a pearly sheen” instead of simply “yellow.” It is important to select words that precisely describe
what is being observed, as a scientist can never provide too much information when making
observations. Rather, lack of information can lead to confusion when making conclusions from
the observations. For example, the words “clear” and “colorless” do not impart the same meaning
scientifically. Colorless means without color, while clear is often, but not always, used to describe
the transparency or the absence of a solid in a solution or mixture.
Many different types of descriptive words may be used to illustrate an observation. For example,
words such as: crystalline, flakes, and chunks, or: opaque, hazy, cloudy, milky, gelatinous, and
muddy are excellent ways to describe the formation of various precipitates in a chemical reaction.
Similarly, a solution may appear cloudy and contain small gas bubbles instead of a precipitate. If
the “cloudiness” sinks to the bottom of a solution, it is likely to contain a solid precipitate. However,
if the “cloudiness” floats to the top of a solution, it is more likely to contain a gas.
It is important to acknowledge the difference between an observation and a conclusion. An
observation is a description of what happened, while a conclusion is the explanation of why
something happened. For example, if a reactant is clear and the product is clear, observations may
state “the reactant was clear” and “the product was clear.” The statement “no reaction happened”
is a conclusion made as a result of observations.
Heating and burning
(combustion) are two separate
processes. While both terms, heating and
burning, involve rising temperatures, the
meanings of the two terms and the processes
by which a rise in temperature occurs differs.
Heating is absorbed internal energy, transferred
to the object via an outside system. For example,
when heating water on a stove the heat is
transferred from the heating element of the stove
to the water. In contrast, burning is the process
of combustion. Combustion is an exothermic
chemical reaction that occurs as a result of the
rapid combination between a substance and
oxygen. Thus, the result of an item is being
heated may differ drastically from the
result of an item being burned.
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Experiment Observations of Chemical Changes
Exercise 1: Observations of a Chemical Change
In this exercise, students will perform a variety of chemical reactions and make scientific
observations to describe the chemical change.
Note: You must wear your safety gloves and goggles throughout the entire exercise. Read all
procedure steps before beginning the experiment.
Note: Silver nitrate will cause the skin to turn black upon contact, so use extra caution with this
chemical.
Procedure
1. Set a sheet of black paper (or black tablecloth) and a sheet of white paper on a table.
2. Set one of the 24-well plates on the table, use scissors to carefully snip off the tips of the pipets,
and set them upright in the wells, using the well plate as a pipet holder. See Figure 2.
Note: When snipping the pipets a drop of chemical may escape the pipet and stick to the scissors.
If this happens, dampen a paper towel and wipe the scissors after each pipet is cut open. This will
prevent any cross-contamination of the chemical pipets.
Figure 2. Well plate with chemical pipets.
3. Set the second 24-well plate on the sheet of white paper and arrange the plate so that the
A1-well is in the upper left-hand corner. See Figure 3.
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Experiment Observations of Chemical Changes
Figure 3. Pipet well markings. The numbers and letters of the pipet well are highlighted in green
to help you identify where the markings are located. Note that well A1 is located in the top,
left-hand corner of the well.
4. In well A1, place 4 drops of sodium bicarbonate (NaHCO
3
) and then add 4 drops of hydrochloric
acid (HCl) to the sodium bicarbonate.
5. Using a clean toothpick, stir the chemicals in the well until mixed.
6. Immediately observe the interaction between the chemicals (use the white and black paper
for backgrounds, as necessary) and record the observations in Data Table 1 of your Lab Report
Assistant.
Note: Make sure to select words that precisely describe what is being observed, as described in
the discussion section of the experiment. Pay special attention to changes in color, odor, light,
temperature, formation of a solid, and formation of a gas.
7. From the observations, make a conclusion (Yes or No) if a chemical change occurred. Record
the conclusion in Data Table 1.
8. Repeat steps 4 through 7 for the remaining 11 reactions in Data Table 1.
Note: If your kit contains IKI indicator: Add 5 drops of IKI indicator to well A2. Record
observations of the solution before mixing. Add 2 drops of starch into well A2. Using a clean
toothpick, stir the chemicals until mixed. Immediately observe the reaction and record your
observations. If your kit contains sodium hypochlorite: Add 2 drops of KI to well A2, and 3
drops of sodium hypochlorite. Using a clean toothpick, stir chemicals until mixed. Add 2 drops of
starch solution to well A2. Stir chemicals with a clean toothpick, record your obserations. For well
B1: In the first step, combine 4 drops of each chemical and make an observation. Then, absorb the
chemical into a paper towel and expose the chemical-soaked paper towel to bright sunlight for
approximately 30 minutes. Use the empty short-stem pipet as needed. Then make the second set of
observations.
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Cleanup:
9. Use paper towels to carefully blot up any chemicals that remain in the well plates, or pour the
chemical mixtures down the sink and flush with a lot of water. Thoroughly rinse out and wash
the 24-well plates, use distilled water for a final rinse, and dry them with paper towels. Place
the paper towels in the garbage. Wash your hands thoroughly with soap and water.
10. Properly dispose of used chemical pipets.
11. Place all equipment back into the lab kit box for future use.
Questions
A. Suppose a household product label says it contains sodium hydrogen carbonate (sodium
bicarbonate). Using your results from Data Table 1 as a guide, how would you test this material
for the presence of sodium bicarbonate?
B. Write the chemical equation for the reaction in well A6.
C. One of the reactions you observed resulted in this product: NaCl + H
2
O + CO
2
(g). What well did
this reaction occur in? Describe how your observations for this reaction support your answer.
D. You found a sample of a solution that has a faint odor resembling vinegar (an acid). To verify
that it is vinegar, you add a few drops of phenolphthalein. The sample turns pink. From this
result, can you assume this sample is indeed vinegar or contains some vinegar? Explain your
answer using your results from Data Table 1.
E. While performing a starch test on several different cookie brands, four tests result in the
typical black color of starch presence, but the fifth gives a yellow-brown color. How might you
interpret this result?
F. You have read that a new brand of hair tonic is supposed to contain lead (an ingredient in
Grecian Formula®). Devise a simple test to confirm the presence or absence of lead in that hair
tonic. Use your observations in Data Table 1 to describe a positive result for this test.
G. Is cutting a cake into 8 pieces a chemical or a physical change? Explain your answer.
H. When a soda is poured into a glass and the soda bubbles, is it the result of a chemical change?
Explain your answer.
I. In well B1, what was the reactant in the second step? Did this reactant cause a chemical
change? Use your observations to support your answer.
J. Think about how phenolphthalein acts as an acid/base indicator. Do your observations in well
A5 support this or contrast what you would expect to happen? Explain your answer.
Exercise 2: Heating and Combustion
In this exercise, you will investigate the results of heating an object and burning an object.
Procedure
1. Put on your safety goggles and gloves.
2. Gather the magnesium metal, copper(II) carbonate (CuCO3), copper(II) nitrate (Cu(NO3)2, and
mossy zinc.
3. Observe the physical properties of the 4 chemicals (color and state of matter) and record in
Data Table 2 of your Lab Report Assistant, under the “Initial Observations” column.
4. Place the 4 test tubes into empty wells of the test tube rack.
5. Use the tweezers to put 1 piece of magnesium into a test tube and 1 piece of mossy zinc into
another test tube.
6. Use the spatula to add a pea-sized amount of CuCO3 into a test tube and a pea-sized amount
of Cu(NO3)2 into another test tube.
7. Place the burner fuel on the pie plate.
8. Uncap the burner fuel and light the wick with the matches or lighter.
9. Use the test tube clamp holder to pick up the test tube containing the piece of magnesium
metal and hold it over to flame to heat the metal in the tube. HOLD THE TEST TUBE SO THE
OPENING OF THE TEST TUBE FACES AWAY FROM YOURSELF OR OTHERS.
10. Observe the effects of heating the magnesium in the test tube and record the observations
in Data Table 2.
11. Repeat steps 9 and 10 for the remaining three chemicals listed in Data Table 2.
12. Read all of the rest of the steps before moving on to Step 13.
13. Using the spatula (for the powders) or the tweezers (for the metal pieces), hold a chemical
in the flame. Hold the tweezers and/or spatula at their farthest points, away from the flame.
Keep all loose clothing and hair away from the flame and substances, and keep flame away
from your face.
a. For powder: Only use a small amount (approximately half the size of pea) of the
chemical on the end of the spatula. See Figure 4. Leave the spatula in the flame until
all of the powder has reacted.
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Experiment Observations of Chemical Changes
Figure 4. Small amount of powder over the flame.
b. For metal pieces: Only use 1 piece of metal, squeezing each with the tweezers, at
the very end of the tweezers. When burning the magnesium, wear sunglasses under
your goggles to protect your eyes. Ensure that each piece of metal is kept over the
aluminum foil or pie plate. See Figure 5.
Safety Note! You MUST wear sunglasses under your goggles when performing the flame test with the
solid magnesium metal. See Figure 5.
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Figure 5. Wearing sunglasses and goggles when burning the magnesium. Substances are held
away from the face, and all substances stay over the pie plate or aluminum foil when they are
burned.
14. Wash the spatula and tweezers after each use, and remember that the spatula and tweezers
will be very hot after putting them in the flame. Ensure that they have cooled before touching
them with your gloved hand.
15. Record the observations for burning each chemical in Data Table 2.
16. Use the small, 2 oz. aluminum cup to extinguish the burner fuel flame. See Figure 6.
● Place the aluminum cup directly over the flame to smother it. The cup should rest on top
of the fuel canister, with little or no smoke escaping.
● Once all equipment is completely cool, remove the aluminum cup and place the plastic
cap back on the fuel. Ensure that the plastic cap “snaps” into place to prevent fuel leakage
and evaporation. The aluminum cup, fuel, and all other materials may be used in future
experiments.
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Figure 6. Extinguishing burner.
Cleanup:
17. Clean all equipment and return to lab kit box for future use.
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Experiment Observations of Chemical Changes
Questions
A. Describe the similarities and/or differences between heating and burning the magnesium
metal. Did either heating or burning produce a chemical change? Explain your answer using
the observations collected in Data Table 2.
B. Describe the similarities and/or differences between heating and burning the mossy zinc metal.
Did either heating or burning produce a chemical change? Explain your answer using the
observations collected in Data Table 2.
C. Describe the similarities and/or differences between heating and burning the Cu(NO
3
)
2
.
Did either heating or burning produce a chemical change? Explain your answer using the
observations collected in Data Table 2.
D. Describe the similarities and/or differences between heating and burning the CuCO
3
. Did either
heating or burning produce a chemical change? Explain your answer using the observations
collected in Data Table 2.
E. How would you describe the differences between heating and burning? Use your experiences
in the experiment to describe these differences.
F. Which of the four chemicals that was heated produced a physical change? Support your answer
with observations made and recorded in Data Table 2.