Summary

In this lab, students will demonstrate their understanding of writing, balancing, translating, and identifying types of chemical reactions. While doing so, they will learn about the process of recycling copper.

Grade Level

High school

AP Chemistry Curriculum Framework

This lab supports the following unit, topics and learning objectives:

• Unit 4: Chemical Reactions
  • Topic 4.1: Introduction for Reactions
    • TRA-1.A: Identify evidence of chemical and physical changes in matter.
  • Topic 4.2: Net Ionic Equations
    • TRA-1.B: Represent changes in matter with a balanced chemical or net ionic equation: a. For physical changes. b. For given information about the identity of the reactants and/or product. c. For ions in a given chemical reaction.
  • Topic 4.7: Types of Chemical Reactions
    • TRA-2.A: Identify a reaction as acid-base, oxidation-reduction, or precipitation.

Objectives

By the end of this lab, students should be able to

• Observe evidence that a chemical change has taken place.
• Describe reactions by writing word equations and balanced chemical equations.
• Identify types of reactions taking place.
• Understand copper is being recycled throughout the experiment.

Chemistry Topics

This lab supports students’ understanding of

• Indicators of chemical change
• Classifying chemical reactions
• Balancing chemical equations

Time

Teacher Preparation: 15 minutes

Lesson: 2 periods (45 min) or 1 block (95 minutes)

Materials

(Per lab group)

• Small test tube
• Two 100 mL beakers
• Test tube rack
• Glass marking pencil
• 1.0 M NaOH (3 mL per each group)
• 1.0 M HCl (3 mL per each group)
• 1.0 Copper (II) nitrate (3 mL per each group)
• Stirring rod
• Aluminum wire (cut to 12 cm)
• Wire cutters
• Hot plate
• Beaker tongs
• Test tube tongs

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
• Consult the SDS for HCl and the SDS for NaOH for additional information.

Teacher Notes

• Instead of having students mark the test tube at 1 cm marks, you may prefer your students to measure 3 mL of each solution.
• This activity works best if students stop after Part 1 and complete the questions specific to the reaction completed before moving on to Part 2, and so on.
• I require students to show me their work from Part 1 before moving on to Part 2 (and etc.) so I can check for misconceptions and/or provide guidance when necessary.
• I personally do not tell students what they are going to see or find while performing the lab. I do, however, point out that a product will have to be the reactant in the next part of the lab. This clarification is helpful for students to understand.
  • Part 1: Copper (II) nitrate is blue and sodium hydroxide is clear. When added together, a precipitate will form and become more electric blue.
  • Part 2: The precipitate, copper (II) hydroxide, is heated until it turns black forming a new solid, copper (II) oxide.
  • Part 3: A clear solution of hydrochloric acid will be added to the copper (II) oxide, and upon stirring should turn back to a blue solution. If it does not turn blue, have students add more hydrochloric acid until it does.
  • Part 4: Aluminum wire will be added to the blue solution. Hydrogen gas will be produced (bubbles will be visible). A single replacement reaction will also occur, allowing copper solid to be formed.

• Students will need to have experience with the following concepts in order to complete this lab:

1. Writing formulas for ionic and covalent compounds.
2. Balancing chemical equations.
3. Identifying the type of reaction as synthesis, decomposition, single replacement, double replacement, or combustion.

• When students “translate” the equation into a sentence, I require students to use the terms atoms, units and molecules. For example:

2NaCl(s) → 2Na(s) + Cl2(g)

Two units of solid sodium chloride decompose to form two atoms of solid sodium and one molecule of chlorine gas.

Atoms are used to represent an element.
Units are used to represent an ionic compound.
Molecules are used to represent a covalent compound.

• In order for students to see what the final product will look like, I have a demo set aside so they can see what will happen in 20-30 minutes.
• Students may also view this copper recycling lab on YouTube, or you may show this to them to review what actually happened. Note, this video shows a different cycle of eight reactions that end up producing pure copper. The first three reactions are the same as the first three reactions in this lab.
  
• This lab was intended for a 90 minute block. If planning on completing over two days, consider having students do the actual lab work on day 1 and focus on translating, writing, balancing, identifying, etc. on day 2.
• This laboratory experience could also be used to introduce limiting and excess reactants as an extension. In the final step of the lab, aluminum metal is added to the test tube resulting in two different reactions. The reaction with excess hydrochloric acid added in the previous step produces hydrogen gas. The second reaction between the excess reactant, aluminum, and the limiting reactant, copper (II) hydroxide, produces elemental copper. This reaction will be complete when the solution turns from blue to clear and elemental copper has collected on the aluminum wire.
• For clean up, I have students empty their waste in a large filtering system (filter with Erlenmeyer flask). Add 1.0 M NaOH slowly while stirring until all the copper has precipitated as the hydroxide. Remove the precipitate and dry, then put into the trash. Slowly, while stirring, add all the waste HCl solution to the filtrate. Then adjust the pH of this mixture between 5 and 9 by adding 1.0 M acid or base, as needed. Pour the neutralized mixture down the drain. Disposal according to Flinn Method #26b.
• As an extension, students could draw a flow chart to illustrate the transformations of copper throughout the lab.

Cross-Disciplinary Extensions

Connect to Reading
Students could read an excerpt from The Disappearing Spoon by Sam Kean. Pages 167-169 of Chapter 10"Take Two Elements, Call Me in the Morning," focuses on the importance of copper in everyday life.