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Lab – Evidence for Chemical Change
One way of knowing that a chemical change has occurred is to observe that the
properties of the products are different from those of the reactants. The new product
can then become a reactant in another chemical reaction. In this experiment you will
observe a sequence of changes that occur when a solution that begins as copper (II)
nitrate is treated with a series of different reactants. All of the reactions will take place
in the same test tube. At each step you will look for evidence that a new substance is
formed as a result of a chemical change. You will also observe heat changes and relate
them to chemical reactions.
Pre-Lab
1. List four types of observations(evidence) that indicate when a chemical change has
occurred.
For each reaction: IDENTIFY the type of chemical reaction, PREDICT the state of
each substance.
2. Copper (II) nitrate + sodium hydroxide copper (II) hydroxide + sodium nitrate
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Type of Reaction:
3. Copper (II) hydroxide + heat  copper (II) oxide + water
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Type of Reaction:
4. Copper (II) oxide + hydrochloric acid  copper (II) chloride + water
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Type of Reaction:
5. Copper (II) chloride + aluminum  copper + aluminum chloride
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Type of Reaction:
6. Hydrochloric acid + aluminum  hydrogen + aluminum chloride
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Type of Reaction:
Procedure
1. Place 50 mL of water into the 100 mL beaker and heat it on a hot plate until boiling.
This will be the hot-water bath you will use in step 6.
2. While the water bath is heating, use the lab marker and ruler to make three marks
on the test tube that are 1 cm apart. Make the marks starting at the bottom of the
test tube and moving toward the top.
3. Add 1.0 M Cu(NO3)2,
copper (II) nitrate, to the
first mark on the test
tube. FIGURE 1
4. Add 1.0 M NaOH, sodium
hydroxide, up to the
second mark on the test
tube. FIGURE 2
5. Mix the solutions with the
stirring rod. Touch the bottom of the outside of the test tube to see if heat is
released. The copper-containing product in the test tube is copper (II)
hydroxide. The other product is sodium nitrate.
6. Put the test tube into the hot-water bath you prepared in step 1. Heat it until no
more changes occur. Record the changes that occur in the test tube. The
products of this reaction are copper (II) oxide and water. Hint: If it doesn’t
turn Black add a few more drops of NaOH.
7. Remove the test tube from the hot-water bath. Turn off the hot plate. Cool the test
tube and its contents for 2 minutes in room-temperature water.
8. Add 1.0 M HCl, hydrochloric acid, to the third mark. FIGURE 3. Mix with the stirring
rod. Remove stirring rod and rinse in tap water. Record the changes that occur in
the test tube. The new products are copper (II) chloride and water.
9. Place a 12 cm piece of aluminum wire in the test tube. Leave it until no reaction is
observed. Touch the bottom of the test tube to check for temperature change.
Record the changes that occur in the test tube. Two reactions take place.
Copper (II) chloride and aluminum produce copper and aluminum
chloride. The aluminum also reacts with hydrochloric acid to form
hydrogen and aluminum chloride.
10. Carefully remove the wire from the test tube with your stirring rod. Decant the
solution down the drain and flush with water. Compare the copper formed to a
sample of copper wire. Record your observations. Solid copper and aluminum
should go in the trash can.
Observations
Reactants
Products
Copper (II) nitrate +
sodium hydroxide
copper (II) hydroxide +
sodium nitrate
Copper (II) hydroxide +
heat
copper (II) oxide + water
Copper (II) oxide +
hydrochloric acid
copper (II) chloride + water
Copper (II) chloride +
aluminum
copper + aluminum chloride
Hydrochloric acid +
aluminum
hydrogen + aluminum
chloride
Evidence of
Reaction
Analysis and Conclusion
1. What is the color of solutions of copper compounds?
2. Heat can be involved in chemical change in two ways, heat can be absorbed or
heat can be released. Cite specific examples, from this experiment, when heat
was a reactant (absorbed) and when heat was a product (released).
3. Write and balance equations for each of the five reactions that occurred, include
states.