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An Investigation Into The Factors Which Effect The Electrolysis Of Copper Sulphate Solution

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An Investigation Into The Factors Which Effect The Electrolysis Of Copper Sulphate Solution



It is known that by passing a constant electric current through an
aqueous copper sulphate solution that the passage of ions through this
solution results in copper atoms being dissolved into the solution
from the anode while positive copper ions (cations) being discharged
at the cathode. Normally anions are discharged at the anode.

The experiment carried out aimed to monitor the quantity of Copper
(Cu) metal deposited during the electrolysis of Copper Sulphate
solution (CuSo4) using Copper electrodes, when certain variables were
changed. It was considered that the following factors could affect the
deposition of Copper metal on the cathode.

1. Time
2. Current
3. Temperature
4. Molarity/Concentration of Solution
5. Quantity of Solution
6. Size of Electrodes
7. Distance between the electrodes
8. The surface of the electrodes

The time was chosen because it is an easy quantity to measure and
record, whilst at the same time maintaining the other variables at a
constant level. The other factors could be observed in later
experiments, should time allow.

PREDICTIONS

It is possible to predict that the relationship will be directly
proportional between the time the current flows and the mass of Copper
deposited on the Cathode (negative electrode). I can therefore predict
that if I double the time of the experiment, I will therefore be
doubling the charge. This statement can be supported by both of
Faraday’s Laws.

Faraday’s First Law of electrolysis states that:

“The mass of any element deposited during electrolysis is directly
proportional to the number of coulombs of electricity passed”

Faraday’s Second Law of electrolysis states that:

“The mass of an element deposited by one Faraday of electricity is
equal to the atomic mass in grams of the element divided by the number
of electrons required to discharge one ion of the element.”

Another piece of scientific theory we can use to support our
predictions is:

At the anode (+): Cu Cu2+ + 2e-

At the cathode (-): Cu2+ + 2e- Cu

The copper at the anode releases copper ions and electrons, which
float in the solution towards the cathode, where the copper ions and
electrons deposit copper onto the cathode.

It was necessary to have a rough idea of how the results would turn
out. This is possible to work out by using a series of simple of
equations:

Ø Charge (C) = Current (A) x Time (sec.)
Ø Moles of Electrons or Faradays = Charge (C) / 96500
Ø Moles of Copper = Moles of electrons or Faradays / ratio=2
Ø Mass = moles x RAM

If the Current is 0.2A and the time taken 5 minutes

Ø Charge = 0.2 x (5x60)
Ø Faradays = 60/96500
Ø Moles of Copper = 0.0006217/2
Ø Mass = 0.0003108 x 64
Ø Mass = 0.0199 grams

If the Current is 0.2A and the time taken 10 minutes

Ø Charge = 0.2 x (10 x 60)
Ø Faradays = 120/96500
Ø Moles Copper = 0.0012435/2
Ø Mass = 0.0006217 x 64
Ø Mass = 0.0398 grams

If the current is 0.2A and the time taken 15 minutes

Ø Charge = 0.2 x (15 x 60)
Ø Faradays = 180/96500
Ø Moles Copper = 0.0018652/2
Ø Mass = 0.0009326 x 64
Ø Mass = 0.0597 grams

If the current is 0.2A and the time taken 20 minutes

Ø Charge = 0.2 x (20 x 60)
Ø Faradays = 240/96500
Ø Moles Copper = 0.002487/2
Ø Mass = 0.0012435 x 64
Ø Mass = 0.0759 grams

If the current is 0.2A and the time taken 25 minutes

Ø Charge = 0.2 x (25 x 60)
Ø Faradays = 300/96500
Ø Moles Copper = 0.0031088/2
Ø Mass = 0.0015544 x 64
Ø Mass = 0.0995 grams

These equations will help to support my predictions, as from these
equations a “theoretical” table of values can be produced and those
can be plotted against the actual result’s obtained. From this
comparison, it will be possible to spot any anomalies in the results
and from this explain why these may have occurred (see EVALUATION).

METHOD

The apparatus was set up as in the diagram below:

Copper Sulphate solution (50cm3) was poured into a small beaker. The
two copper electrodes were thoroughly cleaned using water and steel
wool, to scratch off the layers of copper from previous experiments.
The electrodes were weighed, their masses recorded and placed into the
beaker containing Copper Sulphate solution. The electrodes were
connected to a cell and ammeter. A steady current flowed (0.2 Amps)
and the experiment was stopped at definite times (i.e. 5,10,15,20,25
minutes). At these times the current was switched off and both
electrodes were removed from the solution. They were then washed by
dipping in distilled water, and dried by dipping into propanone (a
highly volatile liquid which readily evaporates) and placed near an
electric heater.

Once clean and dry both electrodes were both carefully weighed and
their subsequent masses recorded.

GRAPH GRAPH GRAPH

CONCLUSION

The results obtained support the prediction that the longer the
current is left to flow, the more Copper metal is deposited on the
cathode. It is now true to say that if the time is doubled the charge
is doubled, and therefore the amount of copper produced. Proof of this
can be seen in the obtained results:

In 10 minutes 0.0405 grams of Copper is produced.

In 20 minutes 0.0810 grams of Copper is produced.

0.0810 grams is exactly double 0.0405 grams.This proves the prediction
that the longer the experiment lasts, the higher the charge and
therefore, the higher the amount of Copper produced.

The actual results produce an almost straight-line graph, showing
that:

Mass of Copper a Time current Flows

Therefore, it has now been proved, through this experiment, that both
of Faraday’s Laws Of Electrolysis are correct.

Faraday’s First Law of electrolysis states that:

“The mass of any element deposited during electrolysis is directly
proportional to the number of coulombs of electricity passed”

Faraday’s Second Law of electrolysis states that:

“The mass of an element deposited by one Faraday of electricity is
equal to the atomic mass in grams of the element divided by the number
of electrons required to discharge one ion of the element.”

It has also been discovered that the copper anode releases copper ions
and electrons, which form copper at the cathode.

At the anode (+):

Cu Cu2+ 2e-

At the Cathode (-):

Cu2++ 2e- Cu

EVALUATION

Although this was a successful experiment, there were some factors of
the experiment, which could have been improved to make it even more
successful. One of these factors could have been the electrodes,
which, even after a good clean were still quite dirty and obviously
still had irremovable substances from previous experiments still
attached to them. If this experiment were to be repeated for a second
time, in need of greater accuracy, it would be imperative to have a
new pair of electrodes, which have never been used before.

Another factor which may have affected the overall outcome of the
investigation, may have been the fact that the practical work of the
investigation was carried over from lesson to lesson, meaning that
variables such as the concentration or the amount of the Copper
Sulphate solution could have changed between lessons. To overcome this
problem, a stock solution of Copper Sulphate should have been made so
as the concentration remained the same at all times. The same
electrodes and equipment should have been used throughout. Also, when
weighing, the same electrical balance should have been used as there
may have been slight differences between the two balances. This is
what could explain the anomaly (“freak” result) in the graph.

I found this investigation very interesting and am looking forward to
investigating more of the variables in this experiment, which may or
may not affect the mass of copper deposited onto the cathode, such as
changing the Current or Temperature variable.

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"An Investigation Into The Factors Which Effect The Electrolysis Of Copper Sulphate Solution." 123HelpMe.com. 24 Apr 2014
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