The given figure shows experimental set-up for electroplating zinc rod with copper metal. Identify A, B and C *
Answers
Explanation:
Step 1: Prepare the Electrode Cleaning Solution
Prepare approximately 20 mL of a 3.4 M NaCl solution in commercial vinegar. Prepare your
solution in a 250-mL beaker. Make sure to calculate the required amount of solid NaCl in your
lab notebook before coming to lab. Use a graduated cylinder for volume. The mass determined to
± 0.2 g is sufficient for this purpose.
Step 2: Prepare and determine the mass of the electrodes
Use steel wool to clean the copper metal anode and the nickel plated steel or brass cathode.
Attach bare copper wire to the cathode so that the object may be completely immersed in the
plating solution. Determine the masses of the anode and the cathode (with the attached copper
wire). Make your mass measurements to the nearest 0.1 mg. The cleanliness of the metal
determines the uniformity of the electroplating. Clean the cathode with scouring powder (i.e.
Comet or Ajax) and a laboratory brush. Handle the object by the edges to avoid finger prints.
Rinse well with laboratory water.
Step 3: Prepare the Logger Pro software.
Check to see that the constant current system is attached to an analog input on the Vernier
interface and that the Vernier interface is connected to the computer. Start up the Logger Pro
software. The constant current system should be automatically recognized by the software and
the current output of the system should be listed at the top left of the data screen. If the current is
not zero, pull down the Experiment menu and choose Zero. The data acquisition rate should be
set to two samples per second using the following steps.
Click on Data Collection icon . Enter 2 samples/second, a Duration of 1000 seconds,
Step 4: Assemble the electrochemical cell
Place a stir bar and 200 mL of copper plating electrolyte into a 250 mL beaker. Place the beaker
on a magnetic stirrer. Wash the anode and cathode in the NaCl/vinegar cleaning solution. Rinse
both electrodes with distilled water and pat dry with a paper towel. Place the 1 cm x 10 cm
copper strip as the anode in the beaker. Bend the top of the anode so that the metal strip is held
near the side of the beaker, Figure 2. Similarly, bend the copper wire on the cathode so that the
metal to be plated is held submerged and away from the magnetic stir bar. Begin gentle stirring
and ensure that the stir bar does not touch the electrodes.
Gently make sure the dial on the constant current system is fully counter clockwise, which
corresponds to the minimum current setting. Attach the alligator clips of the constant current
source to the electrodes. The negative terminal of the constant current system is black and the
positive terminal is red. Which electrode should be attached to the negative terminal? Take care
to prevent the copper plating electrolyte from coming into contact with the alligator clips on the
constant current system. The electrolyte solution is corrosive.
Plug the constant current system wall transformer into an electrical outlet.
Step 5: Electroplate
Click on the green button in Logger Pro. Wait roughly 10 seconds to give a short
stretch in the plot at zero current. Turn the dial on the constant current source until the reading is
in the range of 0.2 – 0.3 amps. Continue electroplating for roughly 700 seconds and then turn the
constant current supply dial to the minimum setting. Click on the red stop button to end data
acquisition.
Use the mouse to highlight the full time span that current flows. Click on the integration icon
to determine the integral under the current curve. Record this value including units. What do
the units correspond to?
The current versus time profile is roughly rectangular. To provide a check of the integral
results, we estimate the integral as the area of the rectangle with height given by the average
current and width the length of time that current flows. Use the mouse to highlight the long-time,
flat portion of your current plot then click on the Statistics icon, . The mean of the selected
data points will be listed. Record this value. Determine the length of time that current was
flowing. Record this value. Compare the area of the rectangle to the integral value. The results
should be similar, however the integral is more accurate, since the current isn’t constant.
Step 6: Determine the mass gained or lost of each electrode.
Rinse the electrodes in deionized water. Gently pat the electrodes dry using a paper towel. Allow
the residual moisture to evaporate for few minutes. Determine the masses of the electrodes.
Determine the mass gained or lost from each electrode. Under ideal conditions, what should be
the relationships between the mass lost by the anode and the mass gained by the cathode?
Clean Up: Return the copper plating electrolyte to the stock bottle for reuse. Use a Q-tip to make
sure that the alligator clips on the constant current system are clean and dry.