Length: 2202 words (6.3 double-spaced pages)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
To find the amount copper gains or loses on the electrodes using
different amounts of current each time during electrolysis. How the
changing of current affects the electroplating of copper.
Electroplating is generally carried out in order to improve the
appearance or corrosion resistance of the surface of a metal by
electrodepositing a thin layer of metal ion on it. The metal substrate
to be coated is made by the cathode in an electrolytic cell. The cell
used in electroplating contains an electrolyte which is usually an
aqueous solution containing a reasonably high concentration of an ion
of the metal which is to be electroplated on the surface. The cell
anode is usually a piece of the metal to be plated from solution; this
enables the anode reaction of metal dissolution to replace the metal
ion lost from solution by the cathodic decomposition.
There are many various factors that affect the mass deposited during
1). Current (A) - An increase in the amount of current increases
the amount of substance deposited in a fixed
amount of time, because there is more energy available to move
ions/electrons to the cathode from the anode. A smaller current will
pump fewer copper ions from the anode to the cathode in the same
amount of mass gained on the cathode is lower.
2). Time - The longer time can let more copper ions from
the anode to the cathode if the current are the
same. There are still more factors which can affect
the mass deposited during electroplating.
3). Distance between two electrodes - If the distance between the two
electrodes is greater, the copper ions
require to travel more from the anode
to the cathode. If the distance between
the two electrodes is smaller, the copper
ions need less energy to flow from the
anode to the cathode
than when the
distance between of the electrodes is far
4). Surface area of electrodes- The surface area of the electrodes
number of ions that can be lost or gained at
the same time. If the surface area of the
anode is greater, there will be more copper
that can be deposited on the cathode.
Therefore the greater surface area; more
more reactions may occur at the same time.
5). Concentration of the electrolyte- When the copper electrodes are
into a concentrated solution, there are
more ions that can be discharged in the
reaction. Therefore, in a higher
solution, there is more
6). Temperature- Temperature can give more energy to the copper to
When the temperature is higher, there is more
available for the copper ions to move from the anode to the
cathode. When the temperature is low, there is less energy
available for the copper ions to move from
the anode to the
I predict that the outcome to be is that as the amount of input
increases, the amount of copper being gained increases. I predict
that, initially a higher current will result in more copper being
transferred onto the cathode, but with a much poorer standard of
adhesion. And that repeats carried out at lower currents will be
characterised by small amounts if better adhered metal being
transferred. The optimum conditions will be a compromise between these
two, a layer of metal plate applied as rapidly as possible yet
maintaining a high degree of adhesion.
I have decided that, since it would be easy to control metal ion
concentration, electrolyte PH, and the nature and amount of all
substances present in the electrolyte simply by mixing one large
reserve of electrolyte, it would be wrong to alter one of these
factors. Another factor affecting electroplating, is the amount of
cathode and anode that is submerged in the electrolyte, in my opinion
it would be easiest to overcome this possible inaccuracy by ensuring
that during all repeats both are completely submerged.
Current and time are both easily varied, and from precious work I know
that current makes a great difference to the way in which the metal is
deposited on the cathode whereas time tends more to effect quantity of
material transferred. Therefore I have decided that the optimum
conditions are most likely to be found through a variation of current.
I will do this whilst keeping all of the other factors as uniform as
possible. I will also carry out a series of pilot test, using the same
method as described for the main procedure to find a suitable range in
which to conduct my repeats. The volume of the concentration of the
electrolyte was decided by doing some small tests in advance and
observing which volume is best for electroplating. I found out that
40cm3 is the correct volume to use for my experiment. I also carried a
few tests to decide the lengths; it was decided by whether the certain
various lengths are best for electroplating. And by my results I found
that 5cm was the best length to use.
· Glass beaker
· 1-24V Power Source
· Variable resistor
· Cable wires
· Top pan balance (accurate to 2dp)
· Copper II Sulphate solution
· Carbon electrodes
1. Connect two terminals of circuit.
2. Attach carbon anode to positive terminal of circuit.
3. Attach carbon cathode to the negative terminal of circuit.
4. Pour 40ml of copper II sulphate into the beaker.
5. Lower cathode and anode into the beaker containing copper II
6. Record masses.
7. These steps are repeated two more times.
8. Next averages are found.
9. These should be put into a table.
From my previous found out, stated out in a table it shows what
figures should be used for the real experiment
The experiment was timed for a fixed time interval of five minutes.
The range of current:
Once the carbon electrodes had been measured and placed in equal
distance in the beaker, and the copper II sulphate solution was there,
the power source was turned on. 0.2A was kept constant for five
minutes so the current does not fluctuate by the variable resistor.
After the five minutes the electrodes were removed from the solution.
Making sure that the reading for the mass is accurate.
The electrodes should not be blown on or wiped, instead they should be
shaken. So this does not interfere with the readings and results. The
surrounding temperature has to be roughly constant through out the
experiment in order to make it a fair test. Also the solution have to
be the same amount, in this case I will be repeating 0.2A, 1.0A and
0.6A twice because they are in order of low, medium and high range of
my experiment and also I could take the average results of them. After
each experiment the electrodes are put into ethanol again to clean the
excess copper sulphate solution, which might affect the change in mass
RANGE OF MEASUREMENTS
My investigation is to see how the different currents affect the
amount of mass of copper deposited. Therefore current has to be varied
in every test. I am going to investigate the current at 0.2A, 0.3A,
0.4A, 0.5A, 0.6A, 0.7A and 1.0A. It is possible to get easily in the
lab, and it can indicate by a normal ammeter as well; it can reduce
the effect of temperature rise in the reaction. The advantage is that
the results will be reasonable results because they are not too high
or not too low. The experiment will be left for five minutes as I
think it is a reasonable tome for the experiment.
· Glass beaker
· 1-24V Power source
· Variable resistor
· Cable wires
· Top pan balance (accurate to 2dp)
· Copper II Sulphate solution
· Copper electrodes
Ø First connect the two terminals of the circuit.
Ø Using the ammeter to measure the current flowing through the
Ø Then use the variable resistor to adjust the resistance of the
circuit to the required current.
Ø Next attach a copper anode to the positive terminal of the circuit.
Ø Then weigh a copper cathode and record its mass.
Ø Then weigh a copper anode and record its mass.
Ø Then attach the copper cathode to the negative terminal of the
Ø Then pour 40ml of copper II sulphate into a beaker.
Ø Then lower the cathode and anode into a bath of copper II sulphate
solution, ensuring that both are fully submerged.
Ø Then leave the circuit complete for five minutes.
Ø Then put two drops of alcohol on the electrodes after removing after
Ø Then allow drying by shaking them.
Ø Then weigh the cathode and subtract the mass from the new mass, then
its area divided it.
Ø Thus is the amount of copper transferred per unit area.
Ø Next weigh the anode and subtract the new mass from its starting
Ø Then is divided by the area of the copper electrode.
Ø This is the amount of copper transferred per unit area.
Ø Then the process is repeated with the same current flow twice, or
until three concordant sets of results are available.
Ø Then the results recording should continue while altering the
Ø Next present the results for every repeat in table form.
Ø Lastly, find the averages.
Copper Sulphate can be toxic and should not be swallowed. Although the
variable resistor will eliminate the danger of shorting, care should
still be taken when working with electricity and liquids, avoid
contact between the two elements. Ineffective electroplating can
produce a finely divided solid of copper, avoid contact between this
and the eyes, and also avoid digesting it. Hands should be washed
thoroughly after each experiment. The usage of safety glasses is
necessary in case of violent reactions occurring and electrical
devices are in operation. The usage of aprons is required as chemicals
may be spoil or stain the clothes of the chemists. Gloves should be
also used due to the usage of chemicals so they do not cause damage to
The ammeter is also a safety precaution to ensure that the current was
not too high, and the current should be controlled and kept at
constant level of decrease or increase. Electric equipment should be
handled with dry hands so that electrocution does not occur. It is
essential to set up the circuit properly, especially to set up the
ammeter; we have to make sure that the positive of the ammeter
connects to the positive of the circuit. And the negative of the
ammeter connect to the negative of the circuit.
From the experiment and by looking at the graph I have presented, it
can be worked put that the amount of change in mass is directly
proportional to the change in current. It is meaning that the amount
of mass lost and gained during the experiment of electrolysis depended
on the amount of charge that is put in so the more you put in the
greater the amount of mass lost and gain.
From the graph when the best-fit line is drawn I can see that they do
line up but for the cathode graph it is not as perfect though. This is
because of some errors had occurred during the experiment. Comparing
to the actual amount of mass lost I am not very far off. The method
and the equation I have mentioned early on in background knowledge can
calculate the actual mass change.
The prediction I have predicted has come out to be exactly the same as
the experiments, which is that the change in mass will be proportional
to the change in current. The graph of the results of the experiment
when compare with the one of the actual mass it looks quite the same
but some are anomalous, the anomalous results were circled in the
graph to distinguish from the other values.
Due to my results, it shows that during the process the anode loses
mass because the copper atoms lose electrons and become copper ions,
Copper atoms à copper ions + electrons
Cu(s) Cu2+ (aq) 2e-
The electrons released at the anode travel around the external circuit
to the cathode. There the electrons are passed on to the copper ions,
Cu2+ (aq), from the copper II sulphate solution and the copper is
deposited or copper plates on to the cathode.
Copper ions + electrons à copper atoms
Cu2+ (aq) + 2e- à Cu(s)
According to my results it showed that when the current increases, the
mass gained on the cathode also increased. They are directly
proportional to each other. The mass gained is directly proportional
to the current in the circuit. It is because when the current is 1A,
there is one unit of electrons that have been discharged, and become
copper cation. These ions have been attracted by the cathode, at the
same time, the gained electrons from the cathode, and become copper
atoms again and deposited on the cathodes.
Cu2+ (aq) + 2e- à Cu(s)
1 mole 2 moles 1 mole
We require 2 moles of electrons to produce 1 mole of copper atoms from
1 mole of copper cations. Also an increase in current means that there
is more resistance which occurs in the solution. This gives out heat,
which is an exothermic reaction. This meaning that there will be more
collisions and more ions with enough activation energy to carry out a
successful collision. Therefore the rate is increased.
I am very pleased about the results that I have obtained. They are
accurate, and they can enable me to prove that the theories in my
predictions are correct. There are several points that I think I have
done quite well to obtain these results. The method, which was used,
was reasonably good and the correct apparatus was used well also. It
was very simple to set up and carry out, using the method which was
chosen. It was simple and safe procedure. But there was room for
Using the purest copper available could also make the results more
accurate. By using a digital ammeter to secure a much more accurate
reading on the current flow. Using the digital rheostat, to keep the
current the same, the sliding rheostat is much harder to use as moving
it to try and establish a constant current flow was very hard. Using
the current rheostat, the current readings were fluctuating and were
complex to maintain its stability. The copper II sulphate solution
should be kept constant and stable.
I would use all the apparatus to its full potential. This would make
my results even more accurate. All my results fitted the pattern. I
would carry out another experiment but this time change the
concentration of copper II sulphate solution every time the experiment
was carried out, but in different concentrations. I would keep all the
other variables the same and see if the change in concentration
affected the mass gained on the cathode.
The experiment went quite well as I expected, except some occasional
errors that have occurred during the experiment. The errors that
occurred causing some of the result to be odd could have been that:
ü The electrodes I used were not the same for some of the experiments.
Since the practicals were done on different days.
ü The starting time was sometimes delayed, which might have caused the
mass to increase.
ü The surrounding temperature was not the same through out the
experiment but theoretically the surrounding temperature does not have
the affect on the decomposition of the solution.
ü The amount of current might have caused the decomposition to be
different because if the amount of current was increased due to the
conductivity of the solution. This will cause the decomposition to
ü The results that I have corrected I think that they are accurate
enough to the actual results to be obtained.
ü It is accurate enough because for some of the experiments I did them
twice to get the average result. This method is the best way to make
the result accurate as possible.
ü The experiments could have been improved by that the rheostat could
have been change to an electric one, which is more accurate and it
would have given better results.