Catalog No. AP6132

Publication No. 6132 Electroplating with Copper Student Laboratory Kit Introduction Coat your keys or another metal object with a thin layer of copper using an electrolytic process called electroplating. Electroplating is a technique used to deposit a layer of metal—such as copper, chromium, silver, gold, or nickel—onto the surface of another metal. The deposit can provide both a protective and decorative coating for the metal which lies beneath it. Chrome plating (on car bumpers) or silver plating (on serving dishes) are common electroplating processes.

Chemical Concepts • Electrolysis/electroplating • Oxidation–reduction • Faraday’s law

Background Electrochemistry is the study of the interconversion of electrical and chemical energy. Two types of cell processes can result in the interconversion of these two energy sources—voltaic cells and electrolytic cells. Voltaic cells use a spontaneous chemi- cal reaction to generate electrical energy. Electrolytic cells use electrical energy (e.g., from a battery) to make a nonspontaneous chemical reaction take place. A nonspontaneous process requires energy from an external source in order to drive the reaction to occur. The electroplating reaction performed in this lab activity is an example of an electrolytic nonspontaneous process. The chemical reactions that take place in electrochemical cells are redox reactions. Reduction occurs at the cathode (negative [–] electrode) and oxidation occurs at the anode (positive [+] electrode). Within an electrochemical cell, positive ions (cations) move toward the cathode and negative ions (anions) move toward the anode. Since the charge on an electron is 1.6022 × 10–19 coulombs and there are 6.022 × 1023 e–/mole, then one mole of electrons carries a total charge of 96,485 coulombs (1 mole e– = 96,485 coul or C). The constant 96,485 C/mol is called the Faraday constant in honor of Michael Faraday, who did extensive research on electrochemical cells. Michael Faraday observed that the amount of substance undergoing oxidation or reduction at each electrode during electrolysis is directly proportional to the amount of electricity that passes through the cell. This is known as Faraday’s Law of Electrolysis. The rate at which electrical charge moves through a circuit is most commonly measured in amperes (amps or A). One ampere of current equals one coulomb of charge passing a given point in one second, or 1 amp = C/sec. Hence, 1 Faraday = 6.022 × 1023 e– = 96,485 C. In the electrolytic cells used in this lab activity, the nonspontaneous oxidation–reduction reactions occurring at the electrodes are the result of the transfer of electrons by the power supply. The power supply acts as an electron pump, pushing electrons into the cathode and removing them from the anode. Electrical neutrality, however, must be maintained; therefore, some process must consume electrons at the cathode and generate them at the anode. The half-reaction occurring at the anode (the copper electrode) is the oxidation of copper to Cu2+. When copper is oxidized to copper(II) ions, two electrons are produced according to Equation 1. – Oxidation at Anode: Cu(s) → Cu2+(aq) + 2e Equation 1 The half-reaction occurring at the cathode (the metal key or object) is the reduction of copper(II) ions to copper. When copper(II) ions are reduced to copper metal, two electrons are consumed according to Equation 2. – Reduction at Cathode: Cu2+ + 2e → Cu(s) Equation 2

IN6132 CHEM-FAXீ. . .makes science teaching easier. 062007 When the combined oxidation–reduction reaction is carried out in an electrolytic (nonspontaneous) cell, the process is called electrolysis (Figure 1).

Power Supply Anode Cathode

Cu Key Electrode

Figure 1. Electrolysis In this laboratory activity, a metallic object (a key) will be electroplated with a copper coating. The energy needed to perform the oxidation–reduction reaction will come from an external power source. The mass change at each electrode (the copper elec- trode and the metal key) will be investigated. The reactions occurring at each electrode will be observed and written. The charge on the copper ion will then be calculated by applying Faraday’s Law.

Materials Copper electrode, 1.2 cm × 15 cm strip Beaker, 50-mL (to clean key) Copper plating solution, 200 mL Beaker, 250-mL Copper wire, 5-cm length (to hold key) DC power supply, variable, low voltage Key (or other metal object such as a coin or a nail) Detergent Sodium hydroxide solution, NaOH, 3 M, 30 mL Glass rod (to support key) Steel wool pad, fine Timer or timing device

Sulfuric acid solution, H2SO4, 3 M, 30 mL Water, distilled or deionized Ammeter, 0–1 A Wires, insulated, with alligator clips (to hook up power supply), 3 Balance, 0.01 g readability

Safety Precautions Sodium hydroxide solution and sulfuric acid solution are corrosive to eyes, skin, and other tissues. Copper plating solution is an acidic solution consisting of cupric sulfate and sulfuric acid; it is moderately toxic by ingestion and inhalation and is a skin and respiratory irritant. Avoid skin contact with all chemicals. Do not operate a power supply with wet hands or in wet areas. Be sure the area is dry before turning on the power supply or closing the circuit. Follow additional safety precautions as appropriate to your power supply. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Wash hands thor- oughly with soap and water before leaving the laboratory.

– 2 – IN6132 © 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Electroplating with Copper, Catalog No. AP6132, from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc. Name: ______Electroplating with Copper Pre-Lab Activity

1. A thin layer of copper will deposit on the key during the electroplating process. What is the source of this copper?

2. What is the purpose of the power supply in the electroplating reaction?

3. Write the reduction half-reaction for the electroplating reaction. Where will this reaction occur?

4. What ions will form at the anode? Write the oxidation half-reaction for the electroplating reaction. Where will this reaction occur?

5. Explain the relevance of the Law of Conservation of Matter to this lab activity.

– 3 – IN6132 © 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Electroplating with Copper, Catalog No. AP6132, from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc. Procedure Part 1. Cleaning the Electrodes 1. Clean a key and a copper electrode by rubbing with fine steel wool. Wash the key and the copper electrode with detergent and rinse both with tap water. 2. Attach a 5-cm length of copper wire to the key. The wire will serve as a handle to remove it from the cleaning solutions and to support it during the electrolysis. 3. Soak the key and copper electrode for a few minutes in 30 mL of 3 M sodium hydroxide solution. Remove the key and rinse it with distilled or deionized water. 4. Soak the key and copper electrode for a few minutes in 30 mL of 3 M sulfuric acid solution. Remove the key and rinse it with distilled or deionized water.

5. Remove the wire from the key. Save the wire for use in Step 9. Glass Rod Dry the key and the copper electrode thoroughly for Part 2. Copper Part 2. Copper Plating the Key Electrode Power Ammeter Supply 6. Determine the mass of the key to the nearest 0.01 g. Determine the mass of the copper electrode to the nearest 0.01 g. Record

.5 both initial masses in the Data Table. 1 0 6 0 + 7. Pour approximately 200 mL of copper plating solution into a + Black Red 250-mL beaker. Note: Copper plating solution is an acidic solution consisting of cupric sulfate and sulfuric acid. Avoid all skin contact. Rinse skin Copper Plating Key Wires immediately if any contact is made. Solution 8. Place the copper electrode into the beaker. Bend the copper strip Figure 2 to fit over the top of the beaker (See Figure 2). 9. Reattach the 5-cm length of wire to the key. Suspend the key in the beaker by wrapping the wire around a glass rod. Rest the rod on top of the beaker. Be sure the copper electrode and key are not touching. 10. Hook up the variable DC power supply. Wire the key directly to the negative (black) terminal of the power supply. Wire the positive (red) terminal of the power supply to the positive terminal of the ammeter. Wire the negative terminal of the ammeter to the copper electrode. 11. Note: Before turning on the power supply, be sure the area is dry. Read the safety precautions on page 2. Turn on the power supply and use a timer to begin timing. Adjust the current to approximately 0.50 amps (A). Monitor the current to maintain a constant reading throughout the electroplating. (Note: Current may vary as the copper is removed from the electrode and plated onto the key.) Record the exact current in A in the Data Table. 12. Turn off and unplug the power supply after approximately 10–15 minutes and stop the timer. Record the exact time for electrolysis in minutes in the Data Table. Convert the electrolysis time to seconds. Record the seconds in the Data Table. 13. Remove the key and copper electrode from the solution. 14. Carefully rinse the key with distilled water and gently pat it dry. Remove the wire from the key. Be careful to minimize the rubbing of the key or some copper may flake off and alter the final mass. 15. Determine the final mass of the key to the nearest 0.01 g. Record the final mass in the Data Table. 16. Rinse the copper electrode with distilled water, dry it off, and determine its final mass. Record the final mass of the copper electrode in the Data Table. 17. Disconnect the wires from the power supply and return the copper plating solution to the reagent table for reuse. 18. Complete the calculations and post-lab questions on page 6. 19. Optional Trial II—Repeat steps 1–18 using another metal object such as a coin or a nail.

Disposal Consult your instructor for appropriate disposal procedures.

– 4 – IN6132 © 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Electroplating with Copper, Catalog No. AP6132, from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc. Name: ______Electroplating with Copper Data and Calculations Table

Data Table Trial 1 Trial 2 (Optional)

Initial mass of key (g)

Final mass of key (g)

Change in mass of key (g)

Initial mass of copper electrode (g)

Final mass of copper electrode (g)

Change in mass of copper electrode (g)

C Current (A or ——) sec

Time of electrolysis (min)

Time of electrolysis (sec)

Calculations Table Trial 1 Trial 2 (Optional)

Coulombs transferred (C)

Faradays transferred (F)

Moles e– transferred

Moles Cu deposited on key

Moles Cu lost by strip

Moles e– transferred per mole Cu deposited on key

Moles e– transferred per mole Cu lost by strip

– 5 – IN6132 © 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Electroplating with Copper, Catalog No. AP6132, from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc. Calculations and Post-Lab Questions Complete the following calculations and questions, showing all work on a separate sheet of paper. Fill in the results in the appropriate spaces in the Calculations Table. 1. What observations suggest that a chemical reaction occurred? 2. Calculate the change in mass of the key and of the copper electrode. Record in the Data Table. Compare the change in mass of the two electrodes. Explain your observations. 3. Calculate the number of coulombs (C), the number of Faradays (F), and the number of moles of electrons (moles e–) trans- ferred by the power supply. Record in the Calculations Table. 4. Use the mass of copper deposited on the key (negative electrode) to determine the moles of copper ions deposited at this electrode (the cathode). Record in the Calculations Table. 5. Use the mass of copper lost by the copper strip (positive electrode) to determine the moles of copper atoms lost at this electrode (the anode). Record in the Calculations Table. 6. What is the ratio between the moles of electrons transferred by the power supply and the moles of copper ions deposited at the cathode (key)? Record in the Calculations Table. 7. Use the result from Question 6 to determine the charge on a copper ion. 8. Write the reduction half-reaction that occurred at the cathode. Relate this reaction to your answer for Question 6. 9. What is the ratio between the moles of electrons transferred and the moles of copper atoms lost by the anode (copper strip)? Record in the Calculations Table. 10. Use the result from Question 9 to write the oxidation half-reaction that occurred at the anode.

– 6 – IN6132 © 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Electroplating with Copper, Catalog No. AP6132, from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc.