By reactive metals are used in a voltaic cell,

By analyzing the results of the first three
experiments, in which the concentration of Copper Sulphate solution is kept
constant, I can conclude that as the difference in reactivity between the
metals decreases, so does the electrode potential between the metals. The
largest reactivity is found between Zinc and Copper, according to the
reactivity series, and thus the largest electrode potential is also found in
the Daniel Cell (Which is a Zinc/Copper Cell) which is 1.6 V. According to the
reactivity series, Iron is less reactive than Zinc and thus, the electrode
potential between Iron and Copper is only 0.82 V which the smallest reactivity
is found between Zinc and Iron and the electrode potential value I measured is
only 0.51 V.

Reactivity is basically a measure of how
strongly at atom gains or loses electrons. A large difference in reactivity
means that one atom tends to gain electrons strongly and one atom tends to lose
electrons strongly. When two very reactive metals are used in a voltaic cell,
then the more reactive metal loses electrons strongly and the less reactive
metal gains those lost electrons strongly. This strong tendency of the
respective metals to oxidize and reduce results in the large electrode
potential of the cell.  As the difference
between the reactivity reduces, one of the metals loses its tendency to gain or
lose electrons strongly. Thus, because of that lost tendency, the electrode
potential recorded for such a cell is lower. For example, Zinc and Copper have
a large difference in reactivity. Zinc tends to lose electrons strongly and
Copper tends to gain electrons strongly. Therefore, this results in a high
electrode potential of the cell. When Copper is replaced by Iron, the oxidizing
ability of Zinc is the same but the reducing ability of the less reactive metal
decreases greatly and thus electrons are not attracted with a very strong force
between the electrodes. Thus, the recorded electrode potential decreases.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

The second part of the practical
investigates the variation of the electrode potentials with a change in
concentration of the electrolytes. According to the results, as the
concentration of the Copper Sulphate solution decreases, so does the electrode
potential of the cell.  However, plotting
these quantities doesn’t result in a line of best-fit, rather it results in a
curve of best-fit, which implies that the quantities are not directly
proportional to each other.

The reason for a variation in the electrode
potential when the concentration of the solution changes is that according to
the equation:

Cu2+
+ 2e– ? Cu(s)

Applying the Le Chatelier’s principle, we can
infer that as the concentration of Copper Sulphate solution decreases, the
reaction tends to shift to the left, attempting to increase the concentration
of Copper ions in the solution. Thus, less of Cu metal would tend to be formed
which would mean that less electrons would be needed, thus implying that the
electrode potential would reduce.

  

Evaluation:

The uncertainty in the experiment is not
very large and is basically due to the uncertainty in the voltmeter. The
percentage error in each of the experiments is

Experiment 1 (Zinc/Copper):

These are the
reactions that are taking place in both the beakers:

In the left
beaker:       Zn (s)                      Zn2+(aq) + 2e

In the right
beaker:     Cu 2+ (aq) +
2e                Cu(s)

Error analysis for this cell:

Observed value: 1.60
V

Literature Value =
Reduction Potential of Copper – Reduction potential of Zinc

                           = 0.34 – (- 0.76) = 1.1 V

Percentage Error:  

 

 

Experiment 2 (Zinc/Iron):

These are the
reactions that are taking place in both the beakers:

In the left
beaker:       Zn (s)                      Zn2+(aq) + 2e

In the right
beaker:     Fe 2+ (aq) +
2e                Fe(s)

Error analysis for this cell:

Observed value: 0.51
V

Literature Value =
Reduction Potential of Iron – Reduction potential of Zinc

                           = -0.44 – (- 0.76) = 0.32
V

Percentage Error:  

 

Experiment 3 (Iron/Copper):

These are the
reactions that are taking place in both the beakers:

In the left
beaker:       Fe (s)                      Fe2+(aq) + 2e

In the right
beaker:     Cu 2+ (aq) +
2e                Cu(s)

Error analysis for this cell:

Observed value: 0.82
V

Literature Value =
Reduction Potential of Copper – Reduction potential of Zinc

                           = 0.34 – (- 0.44) = 0.78 V

Percentage Error:  

 

Since the percentage error in each of the trials is more than
the uncertainty in the results, systematic errors have to be present in the
experiment.

 

One source of error in the experiments using Iron as an electrode is
that the iron nail that I used wasn’t pure Iron. It might have been consisting
of other metals and carbon mixed in it.  This factor is a systematic error. It
increased the electrode potential as can be seen by the results.

 

Another reason for systematic errors in the experiment is the lack
of accuracy in the voltmeter. Since an ideal voltmeter is supposed to have
infinity resistance, the voltmeter I was using didn’t have an infinity
resistance and it also drew current from the circuit which affected the electrode
potential answer we got.

 

Improvements:

To enable the determination of a better
pattern in the graph of Voltage vs. Concentration of the Copper Sulphate
solution, more concentrations between 1 M and 0.1 M could have been experiment
upon so that there is more data in the graph and the graph would be easier to
plot. Another improvement which can be done is that a potentiometer can be used
in the experiment instead of a voltmeter because a potentiometer measures the
voltage using the null method which doesn’t draw in current from the main
circuit. This would mean that the amount of current in the circuit stays the
same.

To improve the accuracy of the results,
more trials could have been taken for each cell setup so that the average of
the results could be taken and the readings would be more accurate.