Electroplating with Copper
2001
In this experiment, we electroplated dried and pressed leaves using copper, a sulfuric acid
(CuSO4(aq)) solution, and an electrical current with an amp reader to measure the amount of
electrons passing through the electrical circuit. I hypothesized that smaller leaves with branchedout shapes would plate more efficiently than large leaves with a lot of surface area. Six leaves of
varying sizes and shapes were plated, and almost all of the leaves yielded between 100% and
140%, with one leaf yielding 58%, and another leaf yielding 170%; thus for the most part the
leaves were yielding over one hundred percent of the theoretical yield. My hypothesis was
proven correct; smaller leaves or leaves with branched out shapes plated more efficiently than
large leaves with a lot of surface area. The observations were recorded in pictures.
The experiment just completed examined the effectiveness of copper electroplating on leaves of
different sizes and shapes. The hypothesis stated that smaller leaves with branched-out shapes
(ie. small oak or ash leaves) would plate better than large leaves with a larger intact surface area
(for example, large maple or cottonwood leaves).
Electroplating is an important part of our everyday lives; circuit boards in computers, telephones,
calculators, and parts of automobiles are often electroplated (Fruen 257). Electroplating,
according to Webster's Dictionary, is to deposit a coating of metal on an object by electrolysis.
Electroplating is putting the use of electrolytic cells to an industrial use. The process requires a
power supply, an amp reader (that measures the level of power of the passing electrons), and a
bath that holds the electroplating solution (Fruen 258). The solution is a solution that allows an
electric current to pass through it. An electric current is a stream of electrons. This is the
essential part of electroplating; if there is no electric current, the electroplating will not work,
hence the name electroplating. In this experiment, the solution being used will be sulfuric acid,
or CuSO4 (Hill 238).
The amount of metal plated onto an object was measured in three units. One Faraday (F) gives
off 6.02 x 1023 electrons (e-), so one mole is equal to one Faraday. One coulomb is the charge of
6.25 x 1018 electrons, therefore one Faraday is equal to 96,500 coulombs. The third measuring
unit is an ampere (amp). It measures the electrical current of 6.25 x 1018 electrons per second,
therefore one amp is equal to one coulomb per second (Fruen 258).
In this experiment, the metal being plated is copper (Cu). This requires an oxidation/reduction.
Cu2+(aq) + 2e- ------> Cu(s)
Cu(s) ------> Cu2+(aq) + 2eThe top equation shows the reduction, and the bottom equation shows the oxidation.
The materials required for this experiment were: a copper-plating bath for the solution, a power
source, an amp reader, three conducting cables to create a circuit that conducts electrons through
the previous materials, a paintbrush, a jar of acetone, a squirt bottle of acetone, a jar of silver
conducting paint, dried and pressed leaves, and a CuSO4(aq) (sulfuric acid) solution made up of
50-248 g/L CuSO4.5HOH, 50—128 g/L 6MH2SO4, 140-33 mL 0.1MHCl, and 5mL/L UBAC
number 1 Brightener (Fruen 260).
The CuSO4 solution was put into the bath. A leaf was painted on both sides with the silver
conducting paint. It was important not to touch the leaf after it was painted because the
fingerprints would have broken the circuit, therefor the electrical current would not have been
able to pass through, and the leaf would not have plated in those areas. The leaf was then
weighed, and the number of grams was recorded.
The cables that made up the circuit ran in this manner: the anodes (positive electrodes, marked
by red) on the bath connected to the anode on the power supply. The cathode (negative electrode,
marked black) connected to the anode of the amp reader. The cathode of the amp reader
connected to the cathode of the bath, which was an alligator clip that held the leaf being plated.
Thus, the leaf was the cathode of the bath. The diagram below shows how the set up looked.
Because the variable being tested was size/shape, not time, each leaf was electroplated for one
hour and thirty minutes. Two pictures were taken of each leaf (one picture for each lab partner)
in order to accurately record the effectiveness of the electroplating.
Six leaves were electroplated in the experiment: a large maple, a large leaf that closely resembled
a cottonwood, a ginko leaf, a small oak leaf, an ash leaf, and a small maple leaf. However, before
the actual experiment was conducted, a birch leaf was used as a test leaf to make certain
everything was in good condition and working order. The test was a success (the leaf plated
beautifully), however, the discovery was made that although the leaf had plated nicely, the amp
reader had malfunctioned. On top of that, the circuit had not been set up correctly. With that
fixed, the leaves were electroplated without complications, with the exception of the ginko leaf,
the third leaf we plated. For a still unknown reason, the copper wire around the leaf plated a great
deal of copper, however the leaf itself plated none. It was therefore removed from the
experiment.
This is the graph of the weight of each of the leaves before the experiment was conducted. The
large Maple weighed 1.092 g; the large unknown weighed 1.270 g; the small Maple weighed
4.604 g; the Oak weighed 1.214 g; the small Ash weighed 0.869 g:
The large Maple weighed 5.109 g; the large unknown weighed 6.038 g; the small Maple weighed
4.604 g; the Oak 5.066g; the small Ash weighed 2.079g. Pictures of the leaves were taken so that
we could accurately record the plating of each leaf. This first picture shows the result of the
plating of the large Maple, large unknown, and small Maple leaves. This second picture shows
the plating results of the Oak and the small Ash leaves.
We decided to test another variable and not make it part of our formal experiment. We did this
test after the experiment was officially over. The CuSO4(aq) solution that we used to plate the
leaves in our experiment was made the previous year for the same experiment. Therefore, we had
been unsure whether or not the solution had enough brightener in it. The leaves had been plating
nicely, however they were not always very shiny. This could mean that we did not have enough
brightner in it, so we added, after the actual experiment was over, 5 mL of UBAC number 1
Brightener. The result was the Oak leaf shown on the left of this next picture. The right leaf is
the test leaf that we used prior to the actual experiment began, in order to test that the equipment
was in working order.
Our results included finding the percent yield of the copper of each leaf, expressed in grams.
This required a series of mathematical equations to first find the theoretical yield which was 3.6
grams. From this, we were able to find the actual percent yield of CU on each leaf. The graph
below shows the percent yield and the theoretical yield for each of the leaves we electroplated
according to the type of leaf:
Conclusion
From the data we collected and the observations made, I found that my hypothesis was proven
correct; the branched-out shapes with less surface area or the small leaves with less surface area
plated better than the large leaves with a lot of surface area. Therefore, based on our results, I
have derived the following statement: at an electroplating time of one hour and thirty minutes
(ninety minutes total), the less surface area to plate, the more efficient the electroplating. Thus
we successfully achieved the desired results needed to satisfy the purpose of the experiment.
The results also conclude that more copper was used to plate the larger leaves (see the Percent
Yield and Theoretical Yield graph above), however those leaves had patches where the
electroplating did not work (see above pictures of electroplated leaves). Either there were
fingerprints on the leaf, thus breaking the electrical circut (however, this does not seem to be the
case), or perhaps because there was a lot of surface area on the leaf to plate, therefore the
electrical current was not as efficient in reaching all areas of the leaf in the time period given to
plate. Perhaps further testing would include varying the time and shape/size, therefore adding an
additional variable to test in the experiment.
Because our leaves were slightly on the dull side after electroplating (with the exception of our
first test-run leaf that was used to test the equipment before the experiment actually started), we
decided to test a theory once the official experiment was over. We decided to add 5mL of UBAC
number 1 Brightener to the sulfuric acid solution. Our test leaf, which we plated before the
experiment began, was very bright and shiny. However, I hypothesized that we used up most of
the remaining brightner in the sulfuric acid with that leaf, therefore the rest of the leaves were
dull. When the experiment was over, we added the 5 mL of UBAC number 1 Brightener and
plated an Oak leaf for one hour and thirty minutes, our control time for the experiment. The leaf
plated brilliantly, showing every vein in the leaf.
Perhaps the idea for a further test would be to challenge the efficiency of different amounts of
brightner in the sulfuric acid. Indeed, our sulfuric acid was made the year before us; we did not
make it ourselves as a part of our experiment. If I were to change the experiment at all, I would
make (time permitting) mixing the sulfuric acid solution a requirement.