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The Effect of the Amount of Sodium Chloride on the Electric Current During Electrolysis

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The Effect of the Amount of Sodium Chloride on the Electric Current During Electrolysis

Background

When an electric current passes through sodium chloride solution,
chemical reactions take place at both cathode and anode. If one passes
through sodium chloride solution, there will be passage of ions moving
through this solution. This results in positively charged sodium ions,
which have been dissolved into the solution, moving towards the
cathode and deposited there. At the same time, negatively charged
chloride ions will be moving towards the anode and discharged at the
anode. This is called electrolysis.

Aim of experiment

My aim is to investigate the effect of the amount of sodium chloride,
i.e. concentration gradient, in the aqueous solution on the electric
current during electrolysis.

Key Factors/ variables that affect the results of the experiment

The experiment carried out aimed to monitor the current during
electrolysis when the amount of sodium chloride was changed. To ensure
a fair test, only one of the listed key variables is allowed to change
at a time with the rest of the variables are kept constant."

This will give me an accurate set of results, which, I hope, enables
me to make a decent conclusion. If we do not control the factors apart
from the concentration we are testing, you can turn around and say
that it was the other factors that had caused the difference and that
it had nothing to do with the concentration. By keeping the factors
controlled and equal, you can prove it is the concentration.

The following factors/variables must be controlled or monitored during
the experiment:

1. Temperature

2. Quantity of solution

3. Voltage

4. Size of electrodes

5. Distance between electrodes

6. Surface on the electrodes

7. Distilled water

I plan to finish the experiment in one day, so the temperature won't
change drastically and use a stop-clock to maintain the time duration
for applying voltage to 10s. By using a volumetric flask and pipette,
I can measure and control the quantity of solution for each test batch
more accurately. To make it fair, I will keep the voltage the same at
5V all throughout the experiment. I will use a variable voltage power
pack to control the voltage at a certain setting during the
experiment. I will use fresh new electrodes from the same pack and use
the same electrode holder to fix the electrodes so the electrodes'
distance and size won't change significantly. Finally, tap water
contains magnesium and other impurities, therefore I will use
distilled water throughout the experiment.

Apparatus and Materials

1. Electrode holder

2. scale

3. crocodile clip

4. graphite rods

5. volumetric flask

6. pipettes 50ml/ holder

7. beakers

8. 4 wires

9. filter

10. voltmeter

11. variable voltage power pack

12. access to distilled water

13. access to NaCl

14. electric supply

15. marker pens

16. spatula

Procedure

First, I checked in the textbook and found that the maximum amount of
salt can dissolve in 1000ml water is 360g at room temperature.

[IMAGE][IMAGE]

Also, from my preliminary work, I found that the current and voltage
for solution with10g NaCl is:

Current(A)

-10.00

-8.00

-6.00

-4.00

-2.00

Voltage(V)

-2.73

-1.88

-1.03

-0.30

0.00

And the current and voltage for solution with 30g NaCl is:

Current(A)

-10.00

-8.00

-6.00

-4.00

-2.00

Voltage(V)

-3.18

-2.25

-1.28

-0.36

0.00

Therefore, I decided to use batches of solution with 5g, 10g, 15g, 20g
and 30g NaCl.

I have to clear the desk first, so I can have more room to do the
experiment. I will also check if the apparatus I am going to use are
clean, to prevent contamination. I will dissolve the 5 different
measures of NaCl into 100ml of water using a volumetric flask. I will
stand them on the bench for 2 days before doing the experiment to
ensure that they have completely dissolved. I will then add distilled
water up to 100ml, because from preliminary work I have noticed that
water will become less than before salt has been dissolved. After
that, I will use a burette to measure exactly 30ml of each NaCl
solution into 3 beakers. So altogether there are 15 beakers. I will
use marker pens to label them carefully to distinguish them easier and
prevent mixing later. Then, I will set up the electric current as
below.

[IMAGE]

I will make my testing fair by doing multiple tests using the same
concentration and keeping the others constant. At the end, I can pool
the results together to get an average. This will reduce the
probability of biased results. I will also record up to 2 d.p. for
more accurate results. I think the range of NaCl concentration that I
have chosen will give me a reasonable set of results for me to
analyse. It will be adequate enough to plot graphs. Also, if I can
spot any anomalous results, I plan to repeat them.

Predictions

I predict that there will be a relationship/correlation between the
current and the mass of sodium chloride. I think that the higher the
concentration of sodium chloride solution the higher the current will
be. This is because the electrolysis of an aqueous solution of sodium
chloride using graphite electrodes will cause transfer of sodium from
anode to cathode and ionization of the sodium chloride is ionised in
the aqueous solution. The higher the concentration, the more
delocalised ions, the quicker they can move around, which results a
higher current.

Obtaining Evidence

Collecting measurements

This experiment is for finding whether my prediction, 'The higher the
concentration of sodium chloride solution the higher the current will
be' is correct. During the process of collecting measurements, I made
sure that all factors listed in the plan, such as temperature, voltage
and distance between electrodes, were kept constant and only the
variable varied. I connected the beaker of sodium chloride solution
with the electric current as in the plan and passed through
electricity.

Safety Precautions

There are some safety precautions I have to beware of, or I will get
myself into potential danger. I realize that chlorine gas is
poisonous; I should not smell the gas for a long period of time. I am
also aware that short circuit might also occur and affect my results.
I have to make sure that the electrodes, wires; crocodile clips etc do
not touch each other. Also, a voltage of 10A is a high voltage. I have
to make sure through out the experiment; the voltage should be less
than 10A. I don't think it's a large problem for me because a chose 5A
for my experiment, unless I accidentally turned it the wrong way, I
should not think that it will happen. Finally as this experiment
involves electricity, electric shocks might occur. I will be careful
and avoid possibilities of getting the shock, for example, using wet
hands to touch the wires and before using the wire, check if it is
safe, i.e. no holes. Sodium Chloride, i.e. salt, is not believed to
present a significant hazard to health. Therefore, I do not need to be
so cautious, but that doesn't mean being careless. I will wear safety
goggles, if the electrolysis reaction is too vigorous.

Evidence Collected

My measurements of the experiment are shown in the table below:

Concentration(g)

First Test(A)

Second Test(A)

Third Test(A)

Average(A)

5.0

0.22

0.22

0.22

0.22

10.0

0.42

0.33

0.31

0.35

15.0

0.54

0.34

0.39

0.42

20.0

0.59

0.38

0.52

0.50

30.0

0.60

0.57

0.58

0.58

I believe that these results to be accurate and reliable as
measurements in the same tests are quite similar and they all go in
sequence. All of the experiments follow the trend that the higher the
concentration, the larger the current. E.g. At 5g, the current is
0.22A and at 30g, the current is 0.58A.

My equipment was used to precision as the current and volume was
record to the nearest d.p. I used the apparatus I listed in the plan,
for example, top-pan balance, it reads to the nearest 2d.p. I made
sure the reading with the container 0g before adding sugar and I
weighed them twice, to check if the measurement was right. I also used
volumetric flask and burettes to measure the volumes. They gave me a
more accurate reading than measuring cylinders, therefore gives a
fairer result. And I also started timing the experiment when the power
current was switched on, to make it fair to all experiments.

I think I have a large enough range of results at different
concentrations to make accurate observations.

However, I noticed that in my second and third test, the measurements
of current with the concentration of 15g and 20g was slightly lower
than my first test. I would like to have repeated it again, but due to
the time, I decided to leave it.

Analysing Evidence and Concluding

Analysing Evidence

By doing the experiment and getting the results, I can state that the
higher the concentration, the higher the current. This is because
there are more particles inside the solution, so when electricity was
inserted, they have more energy and move faster. As there are more
particles at higher concentration, they have less space to move
around. They have more chance of colliding with other particles and
reacting.

[IMAGE]

This graph shows that the higher the concentration, the higher the
current. There are no measurements out of place so I believe I have
completed the experiments accurately.

[IMAGE]

This graph increased less in the concentration of 15-20g. However, it
also agrees generally that it increases.

[IMAGE]

The graph above also shows that the overall trend is increasing. It
levels out earlier than the ones above. The reason it levels out is
because too many ions are in the solution this then results that the
space for every ion is small, therefore they block each other. It is
difficult to transfer anions to anode or cations to cathodes.
Conductivity slows down.

Refer to separate sheet for the graph showing average results.

The graph shows the trend is a reasonably steady upward sloping line.
It is reliable as there are no measurements which are miss fitting to
the line, though there is a slight dip in the concentration of 15g, it
is not big enough to be considered out of place and therefore can be
ignored.

Conclusion

All the graphs show that there is a trend that the current increases
with the concentration. Also, the current will finally level out as
the concentration is high.

Sodium chloride is an ionic compound. It is made up from positive and
negative ions arranged in a giant ionic lattice hold together by
strong electrostatic attraction by opposite charged ion. Each positive
ion (Na+) is surrounded by negative ions and each negative ion (Cl-)
is surrounded by positive ions. Ionic compounds can conduct
electricity when dissolved in water or melted.

The cathode is the electrode connected to the negative of the power
supply. The positive ions are attracted to the cathode, and these ions
gain electrons to become uncharged sodium atoms.

Cathode: Na+(l) + e- [IMAGE]Na (l)

2H+(g) + 2e- [IMAGE]H2 (g)

At the anode, which is attracted to the + electrode, the chloride ion
is attracted. The chloride ions react, giving up their electrons, to
form bubbles of chlorine.

Anode: Cl-(l) [IMAGE]1/2Cl2 (g) + e-

4OH- - 4e- [IMAGE]2H2O + 02

The amount of water contents in the solution does not change after
electrolysis. There are more sodium chlorides in higher
concentrations. This is because more electrons are released and so
conductivity increase.

My prediction is largely correct. However, through the experiment, I
now recognize that the speed of conductivity will go down if
concentration is too high.

Evaluating Evidence

My investigation was overall good enough to make a conclusion because
I gathered a suitable range of results and kept the variables constant
by introducing suitable measures (refer to planning). Most of my
measurements fit in with my prediction: the higher the concentration,
the higher the current. The only result which I believe to be out of
place is the second test, but as I mentioned before (refer to
analyzing evidence), it doesn't affect my overall result.

When I had finished my experiments, I discovered that the reason why
there is a slight inaccuracy is because that after each experiment the
electrodes were not always put back in the same position this may have
affected the results because the ions may have shorter or longer
distance to travel, resulting more or less ions to be deposited or
detached. However, this might not have a great effect, because we have
the electrode holder to hold it. What I am more worried about is that
I used the same pairs of electrode throughout the experiment. The
electrodes contained a different concentration before putting into
another concentration. This might contaminate the solution. I think I
should use a new pair of electrodes when I do the repetitions. Also, I
think I should have used the same top pan balance when weighing, as
there may have been slight differences between the two balances. The
above reasons are what could explain the anomaly in the graph.

To further improve my experiment and add additional conclusive data, I
would test a larger range of concentrations, for example, from 0g of
sodium chloride to 35g of sodium chloride. This would give a larger
range of data for me to analyse and draw a conclusion from. I can
also, use a larger voltage, e.g. 8V. I used 5V in my experiment, but
found that it did not give me a wide range of current. I gathered from
other fellow students' investigations, that 8V has a better result.

I am also quite interested in seeing what time has to do with
electrolysis. I am considering this factor for further work. Actually,
the result I gave in the observation part was my second attempt of
getting the results. At first, I made a mistake by using the same
solution 3 times to get the result. The results decreased after each
attempt, therefore I realize that time must have something to do with
the current. I think this is because if there is more time, the sodium
ions will have more time to deposit. I can also investigate other
variables such as temperature and surface area.

Bibliography

A New Chemistry S Clynes, D J Williams, J S Clarke

Chemistry F O Harriss, H Feguson

Chemistry L D R Wilford, B Earl

Metals Atlantic Europe Publishing

http://homepages.stuy.edu/~bucherd/ch22/Electrolysis.htm

http://cst-www.nrl.navy.mil/lattice/struk/b1.html

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"The Effect of the Amount of Sodium Chloride on the Electric Current During Electrolysis." 123HelpMe.com. 20 Aug 2014
    <http://www.123HelpMe.com/view.asp?id=121635>.




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