Investigate the Mass Changes at Each Electrode During Electroplating and Calculate The

21 Electroplating

Purpose

Investigate the mass changes at each electrode during electroplating and calculate the charge on the copper ion through application of Faraday’s law.

Background

Electroplating is the process of coating an electrically conductive object with a layer of metal using an electric current. The process, also known as electrodeposition, is used to improve the appearance, increase hardness, and corrosion resistance of plated objects.

The cathode (article to be plated) in the electroplating cell is connected to the negative terminal of a direct current power supply. The anode is connected to the positive terminal of the supply. The cathode and anode are immersed in an electrolyte which is an electrically conductive ionic solution. When the power supply is turned on, the metal at the anode is oxidized from the 0 valency state to form positively charged cations. These cations migrate through the solution toward the negatively charged cathode. At the cathode, the cations are reduced and deposit in the metallic, 0 valency state.

Electricity can be measured as a rate of electric current flow called the ampere (A). An ampere is equal to 1 coulomb of charge per second. You can calculate the total amount of charge (C) by multiplying the current flow (I) by the amount of time the current is flowing (t):

C = I*t

We can use the Faraday constant to relate the amount of charge to the number of moles of electrons transferred:

(eq 1)

Where:

I is the current in C/s,
t is the time in seconds and
F is Faraday's constant which is 96,485 C/mol.

In this lab, you will use an application of Faraday’s law to calculate the charge on copper deposited on an object during electroplating using the formula:

(eq 2)

where:

I is the current in amperes,
t is the time the current is applied, in seconds
MM is the molar mass of copper,
96,485 is the Faraday constant (F) and
n is the number of charges per cation of copper

Materials

Equipment
• PASPORT Xplorer GLX / • Support stand
• PASPORT Voltage/current Sensor / • Balance (preferably analytical)
• Buret clamp / • Power Supply, 18 V DC, 5 A
• Graduated cylinder / • Magnetic stir plate and bar
• Beaker, 250 mL / • Alligator clip adapters, 1 set
Consumables
• Copper wire, heavy gauge, 5 - 10 cm / • Copper (II) sulfate, 1.0 M, 250 mL
• Metal spoon or other object to be plated / • Paper towels

Safety Precautions

•   Wear safety glasses and follow all standard laboratory safety procedures

Equipment Setup

1)   Place the beaker containing the copper sulfate solution on a magnetic stir plate and add a magnetic stir bar.

2)   Plug the PASPORT Voltage/current Sensor into one of the sensor ports on the top of the GLX.

3)   Carefully clean and dry the copper wire and spoon. Weigh the wire and spoon and record the mass in your data table.

4)   Use an alligator clip adapter to attach one end of a red banana plug patch cord to one end of the heavy gauge copper wire.

5)   Use another alligator clip adapter to attach one end of a black banana plug patch cord to the end of the handle of the metal spoon.

6)   Wrap electrical tape around the spoon and copper wire near one end to provide insulation. Mount clamps on a support rod and clamp the wire and spoon in place by the insulated portion.

7)   Position the end of the wire and the spoon so they are immersed in the solution in the beaker.

8)   Plug the black patch cord from the spoon into the negative (black) terminal of the power supply.

9)   Connect a red patch cord from the positive (red) terminal of the power supply to the positive (+) jack on the current part of the Voltage/Current Sensor. Connect the red patch cord from the copper wire to the negative (-) jack on the Voltage/ Current Sensor.

10)   The Voltage Sensor leads are not used during this experiment.

Procedure

1)   Turn on the GLX. Be sure a graph of current versus time is displayed.

2)   Press  on the GLX to begin recording data.

3)   Turn on the power supply and adjust the current and voltage until the current reads 0.2 ampere.

4)   Adjust the magnetic stir plate to achieve a reasonable amount of mixing without too much agitation to cause splashing. Make sure the stir bar does not hit either of the electrodes.

5)   Run the electroplating process for 20-30 minutes, then press  to end data recording and turn off the power supply.

6)   Press ,  on the GLX to turn on the area under the curve. Record the value as coulombs in your data table.

7)   Carefully remove the metal spoon and the copper wire and place them on a paper towel. Gently and thoroughly dry the spoon and the wire.

8)   Re-measure the mass of the copper wire and of the metal spoon, and record these values in your data table.

Analyze

Record calculations in your lab notebook as you complete your analysis.

Data Table

Initial mass of copper electrode
Final mass of copper electrode
Change in mass of copper electrode
Initial mass of spoon
Final mass of spoon
Change in mass of spoon
Area under curve (coulombs)
Moles of electrons transferred
Moles of copper transferred

Analysis Questions

1)   Calculate and record the change in mass of the copper wire and the change in mass of the metal spoon.

2)   Calculate the moles of electrons transferred and record your answer in your data table.

3)   Use the mass of copper gained by the spoon to determine the moles of copper deposited on the spoon.

4)   From the results of questions 2 and 3, what is the ratio between the moles of electrons transferred and the moles of copper deposited on the spoon?

5)   Use the information from question 4 to write the reduction half-reaction that occurred at the anode.