Materials Included In Kit

Additional Materials Required

Safety Precautions

Nitric acid is severely corrosive, a strong oxidizing agent and toxic by ingestion and inhalation. Reactions of nitric acid with metals generate nitrogen dioxide, a toxic, reddish-brown gas. Work with nitric acid in a fume hood or in a well-ventilated lab only. Hydrochloric acid is corrosive to skin and eyes and toxic by ingestion and inhalation. Sodium hydroxide solution is a corrosive liquid and can cause skin burns. It is especially dangerous to the eyes. Keep sodium carbonate and citric acid on hand to clean up acid and base spills. Copper powder and magnesium metal are flammable solids; copper powder is a health hazard if inhaled as a dust or fume. Acetone is a flammable solvent. Do not use any flames in this experiment. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles and chemical-resistant gloves and apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash their hands thoroughly with soap and water before leaving the lab.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The recycled copper may be discarded in the trash according to Flinn Suggested Disposal Method #26a. Excess sodium hydroxide solution may be neutralized with acid according to Flinn Suggested Disposal Method #10. Excess hydrochloric acid and nitric acid may be neutralized with base according to Flinn Suggested Disposal Method #24b. The waste solution obtained at the end of Part D is acidic and should be neutralized with base according to Flinn Suggested Disposal Method #24b. Set up an acetone waste beaker to collect the acetone rinses, and allow the solvent to evaporate in the hood according to Flinn Suggested Disposal Method #18a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. The experiments can reasonably be completed in one 50-minute lab period. Many “copper cycle” experiments have been reported in the literature. The specific reactions in this experiment were selected to improve the safety of the experiment and make it feasible to complete the cycle in one 50-minute lab period.
• Concentrated nitric acid is a serious health and safety hazard. Using copper powder in this experiment rather than the more common copper wire or copper foil makes it possible to use 6 M nitric acid as the dissolving reagent. The nitrogen dioxide fumes are substantially reduced with this substitution and the reaction time is still reasonable (about 10 minutes). Copper powder presents a minor dust and inhalation hazard.
• If adequate hood space is not available for Part A, consider doing Part A as a demonstration: Add 90 mL of 6 M HNO₃ to 4.5 g of copper powder in a large Erlenmeyer flask. After all the copper has reacted, add distilled water to make a final volume of 150 mL. Give each student group 10 mL of the solution to use in Part B.

Teacher Tips

• The reaction of copper (in the form of a penny) with concentrated nitric acid is a classic “first demonstration” for many chemistry teachers. The demonstration is a tribute to Ira Remsen’s well-known story of his first experience in chemistry, which has become an enduring symbol of the wonders of discovery. Call or write us at Flinn Scientific to obtain a complimentary copy of Publication No. 10687, “That Remarkable Kind of Action.”

Answers to Prelab Questions

1. Concentrated strong acids, such as hydrochloric and sulfuric acid, are severely corrosive to skin and eyes. What additional hazard arises in this experiment when working with nitric acid? What safety precaution will protect against this hazard?

   Reaction of copper metal with nitric acid generates nitrogen dioxide (NO₂), a toxic brown gas with an irritating odor. Part A should be carried out in the hood to avoid breathing NO₂ vapor.

2. The four-reaction copper cycle featured in this experiment is summarized below. Fill in the blanks to show the reagents that will be used in each step.
   {12795_Answers_Figure_2}
3. The amount of copper obtained at the end of the experiment provides a good test of laboratory technique—each operation must be carried out without losing any copper. In Part B, aqueous copper(II) nitrate will be converted to solid copper(II) phosphate, and the resulting mixture will be filtered. How will you be able to tell that no copper is being “lost” during this step?

   The filtrate will be blue if any residual copper(II) ions remain in solution. In order to avoid losing copper in Part B, the filtrate should be checked to make sure it is colorless.

Sample Data

Answers to Questions

1. Write a balanced chemical equation for each reaction in Parts A–D. Classify each reaction as a single replacement, double replacement and/or oxidation–reduction reaction.

   Part A—Oxidation–reduction reaction
   Cu(s) + 4HNO₃(aq) → Cu(NO₃)₂(aq) + 2NO₂(g) + 2H₂O(l)

   Part B—Double replacement (precipitation) reaction
   3Cu(NO₃)₂(aq) + 2Na₃PO₄(aq) → Cu₃(PO₄)₂(s) + 6NaNO₃(aq)

   Part C—Double replacement (acid–base) reaction
   Cu₃(PO₄)₂(aq) + 6HCl(aq) → 3CuCl₂(aq) + 2H₃PO₄(aq)

   Part D—Single replacement (oxidation–reduction) reaction
   CuCl₂(aq) + Mg(s) → Cu(s) + MgCl₂(aq)

2. Determine the mass of copper recovered at the end of the “four-reaction copper cycle” and calculate the percent recovery.
   {12795_Answers_Equation_4}
   Mass of copper (final) = 41.44 g – 41.23 g = 0.21 g
   Percent recovery = (0.21 g/0.29 g) – 100% = 72%
3. List at least three sources of experimental error that might lead to a mass of recovered copper less than that originally used. Be specific! The following errors will lead to a mass of copper less than that originally used.
   1. Not all of the copper powder reacted with nitric acid in Part A.
   2. Some soluble copper(II) compound(s) remained dissolved in the filtrate in Part B.
   3. Not all of the filtered copper(II) phosphate solid dissolved in hydrochloric acid in Part C.
   4. Not enough magnesium was added or not enough time was allowed for all of the copper(II) chloride to react in Part D.
   5. Any material was physically lost in the transfer steps in Parts A–D.
4. List at least three sources of experimental error that might lead to a mass of recovered copper greater than that originally used. Be specific.

   The following errors will lead to a mass of copper greater than that originally used.

   1. The final copper sample is wet.
   2. The final copper sample has been oxidized in moist air to CuO (due to a trace of acid remaining behind after washing).
   3. The final copper sample is contaminated with magnesium because the excess magnesium was not dissolved at the end of Part D.

References

This activity was adapted from Flinn ChemTopic™ Labs; Vol. 6, Chemical Reactions; Cesa, I., Editor; Flinn Scientific: Batavia, IL (2004).

Introduction

How old is the copper penny in your pocket? It may be older than you think! Not only is copper one of the most widely used metals, second only to iron in annual consumption, it is also the most widely reused metal. Almost as much copper is recovered every year from recycled copper scrap as is produced from newly mined copper ore. What reactions can be used to recycle or recover copper metal?

Concepts

• Oxidation–reduction
• Single replacement
• Double replacement
• Percent yield

Background

Copper is a reddish-brown metal with excellent electrical and thermal conductivity. Traditional applications of copper include its use in electrical wiring and plumbing. The modern electronics industry also uses copper to make computers run faster and last longer. Copper is the best choice for these applications because it does not oxidize in air or corrode as fast as most other metals.

Oxidation of copper requires concentrated nitric acid, a strong acid that is also a good oxidizing agent. Copper reacts with nitric acid to form copper(II) nitrate, a blue-green ionic compound that is soluble in water (Equation 1). Copper(II) nitrate, in turn, can be converted into other copper compounds via double replacement reactions with a precipitating agent, such as sodium hydroxide (Equation 2). Copper metal can be regenerated or recovered from copper(II) compounds by single replacement reactions with a more reactive metal, such as zinc (Equation 3).

Oxidation of copper

Experiment Overview

The purpose of this experiment is to carry out a sequence of chemical reactions illustrating the properties of copper and its compounds. The “copper cycle”—which starts with copper and ends with copper—demonstrates how copper might be recycled or recovered from copper scrap. The percent recovery of copper will be determined and the efficiency of the four-reaction copper cycle will be analyzed.

Materials

Prelab Questions

Read the entire Procedure and the recommended Safety Precautions before answering the following questions.

1. Concentrated strong acids, such as hydrochloric and sulfuric acid, are severely corrosive to skin and eyes. What additional hazard arises in this experiment when working with nitric acid? What safety precaution will protect you against this hazard?
2. The four-reaction copper cycle featured in this experiment is summarized below. Fill in the blanks to show the reagents that will be used in each step.
   {12795_PreLab_Figure_1}
3. The amount of copper obtained at the end of the experiment provides a good test of laboratory technique—each operation must be carried out without losing any copper. In Part B, aqueous copper(II) nitrate will be converted to solid copper(II) phosphate, and the resulting mixture will be filtered. How will you be able to tell that no copper is being “lost” during this step?

Safety Precautions

Nitric acid is severely corrosive, a strong oxidizing agent, and toxic by ingestion and inhalation. Reactions of nitric acid with metals generate nitrogen dioxide, a toxic, reddish-brown gas. Work with nitric acid in a fume hood or in a well-ventilated lab only. Hydrochloric acid is corrosive to skin and eyes and toxic by ingestion and inhalation. Sodium hydroxide solution is a corrosive liquid and can cause skin burns. It is especially dangerous to the eyes. Notify the teacher and clean up all acid and base spills immediately. Copper powder and magnesium metal are flammable solids; copper powder is a health hazard if inhaled as a dust or fume. Acetone is a flammable solvent. Do not use any flames in this experiment. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles and chemical-resistant gloves and apron. Wash hands thoroughly with soap and water before leaving the lab.

Procedure

Part A. Copper and Nitric Acid

1. In a 50-mL beaker, weigh out 0.25–0.30 g of copper powder. Record the mass of copper to the nearest 0.01 g in the data table. Place the beaker containing the copper in a fume hood.
2. Using a Beral-type pipet, transfer 6 mL of 6 M nitric acid into a graduated cylinder. Add the acid slowly and carefully to the copper powder in the beaker.
3. Observe the evidence for the chemical reaction and record all observations in the data table.
4. Gently swirl the beaker to make sure all of the copper reacts. When the copper metal has dissolved, add 5 mL of distilled water to dilute the solution.
5. Take the beaker to the lab bench for Part B. Caution: Do not remove the beaker from the hood until all reddish-brown fumes have completely disappeared.

6. Neutralize the acidic copper(II) nitrate solution: Slowly add 6–7 mL of 6 M sodium hydroxide with constant stirring until the mixture is slightly cloudy. Note: A pale blue solid may precipitate out initially when the base is added. The precipitate should redissolve with stirring.
7. Test the solution with pH paper—the solution should be neutral or slightly acidic (pH 6–7).
8. Measure 10 mL of 0.3 M sodium phosphate into a clean, graduated cylinder and add the solution to the aqueous copper(II) nitrate in the beaker. Stir to mix thoroughly.
9. Observe the evidence for the chemical reaction and record all observations in the data table.
10. Fold a piece of filter paper into a funnel and filter the reaction mixture into a clean Erlenmeyer flask.
11. Wash any traces of solid from the beaker into the funnel using a gentle stream of distilled water from a wash bottle.
12. Rinse the solid with about 5 mL of distilled water and discard the filtrate (liquid). Save the solid in the funnel for Part C.

13. Place a clean 125-mL Erlenmeyer flask beneath the filter funnel.
14. Slowly and carefully pour 20 mL of 3 M HCl directly into the funnel and collect the filtrate in the Erlenmeyer flask.
15. Observe the evidence for the chemical reaction and record all observations in the data table.
16. When all of the solid has dissolved, rinse the filter paper with about 5 mL of distilled water. Collect the rinse water in the same flask as the filtrate and save the filtrate for Part D.

Part D. Copper(II) Chloride and Magnesium

17. Prepare a boiling water bath for use in step 26: Half-fill a 250-mL beaker with tap water, add a boiling stone, and heat the water to a gentle boil on a hot plate.
18. Obtain about 0.5 g of magnesium turnings on weighing paper and add the magnesium to the filtrate from Part C.
19. Observe the evidence for the chemical reaction and record all observations in the data table.
20. Swirl or stir the flask for 5–10 minutes until the liquid is colorless. If necessary, add another piece of magnesium to the flask to make sure the reaction is complete.
21. When the copper(II) chloride color has faded to colorless, add an extra 3 mL of 3 M hydrochloric acid to the flask. The acid will react with any leftover magnesium (but not with the copper).
22. When the gas bubbling subsides, decant (pour off) most of the liquid into a waste beaker. Use care to avoid losing any copper during this process.
23. Wash the copper with about 10 mL of distilled water and discard the wash water in the waste beaker.
24. Weigh a clean and dry evaporating dish and record the mass in the data table.
25. Use a gentle stream of water from a wash bottle to flush the copper from the Erlenmeyer flask into the evaporating dish.
26. Allow the copper to settle, then use a pipet to remove as much of the water as possible from the evaporating dish.
27. Rinse the copper metal with two 5-mL portions of acetone. Remove the acetone rinses using a pipet.
28. Place the evaporating dish over the boiling water bath and heat the copper to dryness.
29. Use tongs to remove the evaporating dish from the boiling water bath and place the dish on paper towels. Allow the dish to cool to room temperature and then thoroughly dry the dish using a paper towel.
30. Weigh the dry evaporating dish with the recovered copper and record the combined mass in the data table.
31. Dispose of the reaction product and any waste solutions as directed by the instructor.

Student Worksheet PDF

12795_Student1.pdf