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 àcopper (II) hydroxide + sodium nitrate

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Type of Reaction:

3.  Copper (II) hydroxide + heat à copper (II) oxide + water

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Type of Reaction:

4.  Copper (II) oxide + hydrochloric acid à copper (II) chloride + water

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Type of Reaction:

5.  Copper (II) chloride + aluminum à copper + aluminum chloride

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Type of Reaction:

6.  Hydrochloric acid + aluminum à 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 / Evidence of Reaction
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

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.