Requirements:
-
water bath (30oC)
-
100cm3 1.0M aqueous copper (II) sulphate
- 2 same-sized copper electrodes (6.90 x 3.00 cm)
- 3 d.p. balance
- Burette
- Voltmeter
- Ammeter
- Rheostat
- thermometer in water trough
- safety goggles
- DC power pack
- connecting leads, including two fitted with crocodile clips, 3
- Stop clock
- Balance (3 d.p.)
- Hot-air blower, such as a hair drier
- Emery paper
- Paper towels or tissues
Apparatus:
Technical Notes
- It is difficult to avoid fluctuations in current throughout the electrolysis, and thus obtain an accurate value to use in the calculations
- Be careful to avoid any movement of the electrodes during the electrolysis.
- Thorough washing and drying of the electrodes is vital. A tiny amount of moisture left on the electrodes causes a considerable error in the mass calculations.
- The coating of solid copper on the cathode tends to be ‘spongy’ and some can be lost when electrode is washed or dried. Some may also have fallen off the cathode during electrolysis. Thus the mass gain of the cathode is an unreliable measure of the quantity of copper actually deposited there.
- Current was on average 0.35A, maintained by the rheostat
- Voltage was assumed to stay constant at 6.0V
Method:
- The apparatus was set up as shown in diagram
- The power pack was set to 6.0 volts, and was started simultaneously with the stopwatch
- Every five minutes, the power pack was turned off and the cathode removed
- It was washed with distilled water into a separate beaker to eliminate any remains of the copper (II) sulphate solution
- The cathode was then dried and weighed on a 3-decimal-placed balance to measure the addition in mass
- This was then recorded, and the cathode was put back into the solution, ready to be electrolysed for another five minutes
- This process was repeated for 45 minutes
Results:
Raw Data:
Initial Mass of Cathode = 8.458g ±0.001g
Processed Data:
Uncertainties:
Total Uncertainties affecting Results = 4.58%
(the voltmeter error does not affect result, as it is not a component in the equation being used)
Gradient:
The gradient can be calculated from the graph. I am using the points at 0 and 1500 seconds because they are the easiest to identify the time for.
Gradient = (change in mass of cathode) / time
= 0.190 – 0 / 1500 - 0
= 0.190 / 1500
= 1.27 x 10-4
Faraday’s Constant:
I am using, again, the results obtained for 1500 seconds.
Faraday’s constant = (I . t . M) / (n . w)
= (0.35 . 1500 . 63.55) / (2 . 0.190)
= 87,799.34 C mol-1 ± 4.58%
Conclusion:
From my data and calculations, I determined Faraday’s Constant to be 87,799.34 C mol-1 ± 4.58%. However, the accepted value for Faraday’s Constant is 96,485.34 C mol-1 . My result is 9.0% lower than the acknowledge value, but this is higher than the percentage error I calculated, so, therefore, my result would not be accepted as accurate. The largest error, which could be the cause of this inaccuracy, is produced by the ammeter
Evaluation:
