Measuring the Effects of Current on the Change in Mass of a Penny and a Quarter During Electrolysis

Transcription

1 Measuring the Effects of Current on the Change in Mass of a Penny and a Quarter During Electrolysis

2 Purpose: The objective of this lab is to determine the effect of amperage on the change in mass of a quarter (cathode) and a penny (anode) during electrolysis in a.1m copper (II) sulfate solution by creating a electrolytic cell. Hypothesis: As amperage increases then the change in mass will increase. The rationale for this hypothesis is because as more electrons flow through the electrolytic cell the more ions will be reduced or oxidized. Variables: Independent Variable: Amperage (0.06; 0.08; 0.1; 0.12; 0.14) Dependent Variable: Change in mass of the quarter (cathode) and the penny (anode) Controlled Variables: Temperature, Concentration of solution, Surface area of cathode and anode, Amount of solution, Distance between anode and cathode, and Time Temperature was controlled by performing the experiment in the same room on the same day when temperature was the same. The concentration of the solution was controlled by creating and using a.1m solution of copper (II) sulfate. The Surface area of the cathode and anode were controlled by measuring the midline of each coin, marking it, and then dipping one half below the solution. The amount of solution was controlled by using a graduated cylinder to measure out 100mL of solution. The distance between the anode and the cathode was controlled by taping the coins to the wall of the beaker at their furthest point apart (7 cm). Time was controlled by leaving the current on for 1 minute at each increment for each test.

3 Materials: 15 U.S Quarter 15 U.S Penny (Minted Prior to 1982) 250mL Beaker 500mL Distilled Water g Copper (II) Sulfate (F.W of g) Ammeter 75W AC/DC Power Supply Rubbing Alcohol Masking Tape 100mL Graduated Cylinder 500mL Volumetric Flask Digital Balance 1 Banana Plug Wires (Red) Alligator Clip to Banana Plug Probe Cables (1 Red, 1 Black) Paper Towels Permanent Marker Stopwatch Procedure: mL of distilled water was measured out in a 500mL volumetric flask g of copper (II) sulfate pentahydrate was measured out using the digital balance. It was then poured into the volumetric flask, covered, and then mixed thoroughly. 3. All pennies and quarters were cleaned using rubbing alcohol and a paper towel to get off any surface grime or dirt. 4. The midline of each quarter and penny was then measured and marked using a permanent marker. The diameter of the penny was 19mm and the quarter was 24mm. 5. The mass of each penny and quarter was each measured and recorded. The coins were then placed on a paper towel one at a time after being weighed and numbered in pairs with their initial masses written underneath. 6. Next, the electrolytic cell was put together using the power supply, all 3 wires, the ammeter, the 250mL beaker, and the masking tape.

4 a. First, the power supply was placed on the lab bench and the black alligator clip to banana plug probe cable was plugged into the black (negative) dc plug on the power supply. b. Then the red banana plug probe to banana plug probe cable was plugged into the red (positive) dc plug on the power supply. The other end was then plugged into the.1a plug of the ammeter. c. The remaining wire, the red alligator clip to banana plug probe, was then plugged into the outlet plug of the ammeter. d. Next, the beaker was filled with 100mL of the.1m solution of copper (II) sulfate. e. The two alligator clips wires were then taped to the rim of the beaker at the furthest point apart (7cm) so that the clips hung down to just above the solution. 7. A penny was then attached to the red (positive) alligator clip and submerged in the solution to its midline. 8. A quarter was then attached to the black (negative) alligator clip and submerged in the solution to its midline. 9. The power supply was then plugged in and turned on. The knob was then turned until the amperage reached.06 amps on the ammeter and the stopwatch was started. After 1 minute the power supply was turned off. 10. The coins were then removed from the solution and placed on a paper towel to dry. Once dried their mass was then measured and recorded. This process was then repeated so that there were 3 trials for this increment. 11. The solution was then disposed of and refilled by another 100mL of the.1m copper (II) sulfate solution for a new increment. 12. Steps 7 to 11 were then repeated for increments 0.08; 0.10; 0.12; and 0.14

5 Diagram: Raw Data: Initial Mass of Final Mass of Initial Masss of Final Mass of Raw Data for Electroplating Number Penny (g) Penny (g) Quarter (g) Quarter (g) of a Quarter of (±0.0001g) (±0.0001g) (±0.0001g) (±0.0001g) 0.06 Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps (Amperes) (±0.005)

6 Observations: At the end of each trial, the penny had a lighter color and was visibly stripped of some of its surface. The quarters for each trial had plating; however, past 0.06 amps the color was black instead of the copper color. At 0.10 amps and up there was precipitation around the quarter; however, it didn t plate to the quarter and was floating around in solution. Processed Data: Change in Mass of the Penny and Quarter Following Electrolysis Number of Change In Mass of Penny (g) (±0.0002g) Change In Mass of Quarter (g) (±0.0002g) 0.06 Amps (Amperes) (±0.005) Amps Amps (Amperes)(±0.005) Amps Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps Amps (Amperes)(±0.005) Average Change In Mass of the Penny and the Quarter Following Electrolysis Average Change In Mass of Penny (g) (±0.0002g) Average Change In Mass of Quarter (g) (±0.0002g) 0.06 Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps Amps (Amperes) (±0.005) Amps (Amperes) (±0.005) Amps Amps (Amperes) (±0.005)

7 Conclusion: The purpose for doing this experiment was to determine the effect of current (amperage) on the electroplating of a quarter using a penny and.1m copper (II) sulfate solution. The data above suggests that as current increases the mass plated on the quarter increases. This is what was originally hypothesized. The data in the above graphs appears to have a general

8 linear trend suggesting a direct relationship, however since as current increased there was some mass that was lost to solution this isn t certain. Using the mass lost by the penny would better suggest a linear relationship between the current and the mass lost/plated. Evaluation and Improvements: There are several weaknesses to this experiment. These include human error, random error, procedural error, and measurement error. The first of these, human error, came into play in the creation and execution of the electrolytic cell. While the attempt was made to keep the distance between and the surface area of the two coins constant; it was difficult to do so because over time the tape weakened, or occasional bumps to the table resulted in changes to these variables. This error could be eliminated or reduced by completely submerging the coins into solution to keep the surface area constant as well as using clamps to keep the wires in place instead of tape which sagged over time and the distance between the two coins changed. Random error occurred during the actual time that the power supply was on. This error includes that the needle of the ammeter would fluctuate randomly and the power supply would have to be adjusted mid trial; also there was random error in the trials in which some mass precipitated but didn t stick to the quarter, this caused false values. The first type of error could be improved by using a digital ammeter or power supply to control amperage instead of a manual one. The second error could be improved by using wire mesh or a spatula to fish out the precipitate and add that to the weight change. Procedural error could have occurred during the creation of the.1m copper (II) sulfate solution as well as the cleaning of the coins. The solution appeared to be settling over time and perhaps could have changed by the time the beaker was refilled for the later trials; the coins could have differed in their cleanliness which would result in varying surface area that was clean. The certainty of the solution

9 could be improved by creating it as needed for each trial or by using a test to check its molarity. The cleanliness of the coins could have been improved by being more thorough in cleaning. Lastly, measurement error could have occurred in the weighing of the coins and in the measuring of their surface area. The measuring of the weight of the coins could have been improved by using a more accurate scale, by allowing them to air dry over time, and by adding the lost precipitate to the quarter for final measurement. The measuring of the surface area exposed to solution could have been better measured by using calipers or by simply entirely submerging the coins in solution.