Making the Best Copper Mirror
Lucas Erickson and Adam Yock
2003
Abstract
For this project, the goal was to determine the best copper mirror by observing the
temperature that produced the most copper and which mirror visually looked the most
appealing. We assumed that a higher temperature water bath would produce a more
brilliant mirror as well as the most copper, since the chemicals would react faster. We
mixed nitric acid, glyoxal, silver nitrate solution, stannous chloride solution, and
Fehling’s solution A and B in a glass vial. We then placed the vial into a water bath a
range of temperatures from 11.9°C to 98.9°C. The data suggests that the best copper
mirror is formed when the water bath was close to 53.0°C. The brilliance of the mirror
followed a similar pattern, reaching its peak at 53.0°C.
Introduction
The purpose of this project was to discover what conditions would produce the best
copper mirror. We hypothesized that the temperature of the warm water bath and the
quality of the mirror are directly related. As the temperature increased, so would the
quality of the mirror. We believed that this would happen because the hotter temperatures
would cause the water molecules to move faster causing the chemical reaction to speed
up and produce more copper. We also believed that while the hotter water baths would
produce more copper due to the increased speed of the chemical reactions, the copper
precipitate would accumulate, providing a shinier, more brilliant mirror.
Background
Nitric acid, glyoxal, Fehling’s solutions A and B, as well as silver nitrate solution, and
stannous chloride solution all have important roles in the chemical reactions taking place
within the glass vial. Each chemical and its individual properties contribute to the copper
mirror.
Nitric acid is a strong, colorless liquid with a density of 1.52 grams at 25°C (1). Nitric
acid, HNO3, is a strong oxidizing agent. Nitric acid is manufactured by the Oswald
Process. When ammonia (NH3) is catalytically oxidized at high temperature (900 °C)
over a platinum-rhodium catalyst, nitrogen monoxide gas is formed (NO). The nitrogen
monoxide then cools down and reacts with oxygen (O2) to produce nitrogen dioxide
(NO2). When the NO2 reacts with water (H2O) and oxygen, 60% nitric acid is produced
(2). Cuprous oxide (Cu2O) reacts with nitric acid (HNO3), to form cupric nitrate
(Cu(NO3)2), and copper solid, Cu (s). The production of 90-100% nitric acid is based on:
the reaction of sulfuric acid (H2SO4) with sodium nitrate (NaNO3) the oxidation of
nitrogen dioxide (NO2) in a solution of nitric acid (1). In our project, the nitric acid, as
does the steel wool, serves to clean the vial, preparing it for the oxidation-reduction
reactions. The main oxidation-reduction reaction that takes place in our experiment is
between glyoxal and copper (see Equation 1) (3).
Equation 1: The oxidation-reduction equation of our experiment.
C2H2O2 (aq) + Cu2 + (aq) 2OH- (aq) ---> Cu (s) + C2H2O3 (aq) + H2O (l)
Glyoxal is an aldehyde that is oxidized to a carboxylic acid called glyoxylic acid in our
project (3). Glyoxal is a liquid with no coloring with a formula of C2H2O2 and a
molecular weight of 58.04 grams/mole (4). Not only possessing high reactivity, along
with stabilizing and cross-linking abilities, glyoxal is also miscible in water. It has a six
month shelf life and can irritate the eyes and skin (5). In our project, the glyoxal is
reducing agent as well as being oxidized (see Equation 2) (3).
Equation 2: The C2H2O2 (aq) half equation. The C2H2O2 (aq) is oxidized and is the
reducing agent.
C2H2O2 (aq) ---> C2H2O3 (aq) + 2eFehling’s solution, when reacted with an aldehyde (in our case glyoxal) reduces Cu2+ to
Cu (I) as found in Cu2O (s). In our project, with quite a large glyoxal concentration,
copper is produced from further reduction. The Cu2+ is an oxidizing agent and is also
being reduced in the chemical reactions that take place in our project (see Equation 3) (3).
Equation 3: The Cu2+ (aq) half equation. The Cu2+ (aq) is reduced and is the oxidizing
agent.
2e- + Cu2+ (aq) --->Cu (s)
The purpose of both the silver nitrate solution and the acidified stannous chloride solution
is to coat the inside of the vial with a thin layer of silver onto which copper deposits
create the copper looking mirror (3).
Procedure
1) First, we made stannous chloride solution by mixing 5.64 grams of stannous chloride,
with 250 mL of 12 M HCl, and 250 mL of distilled water.
2) Then, we made Fehling’s Solution A by massing 7 grams of cupric sulfate and
dissolving it into 100 mL of distilled water.
3) After that, we made Fehling’s Solution B by massing 35 grams of potassium sodium
tartrate and 15.4 grams of sodium hydroxide, and dissolving it in 100 mL of distilled
water.
4) Then, we used steel wool to vigorously roughen the inside of a glass vial.
5) Next we massed the glass vial.
6) Next, we rinsed the vial with 4 mL of 15.8 M nitric acid and then with distilled water.
7) Following that, we rinsed the vial with 1 mL of the acidified stannous chloride solution
from step one.
8) We then rinsed the vial with 1 mL of 0.06 M silver nitrate solution.
9) After that, we mixed 2 mL of Fehling’s solution A with 2 mL of Fehling’s solution B
and added the mixture to the vial.
10) Next we added 1 mL of 40% glyoxal, which we purchased from Flinn Scientific Inc.,
to the vial with the solution in it.
11) Then, we placed the vial with the solution into a warm water bath kept at about 50°C
for 5 minutes.
12) After that, we poured the solution out and rinsed the vial with water.
13) We then let the glass vial dry.
14) When the vial was dry, we massed it again.
15) At this point we would also note the brilliance of the copper mirror produced using a
scale of 0-10 with 10 being the most brilliant.
16) Next, we repeated the experiment from steps 4-15 so we would have two trials at
50°C.
17) After that, we repeated this entire procedure, this time using warm water baths with
temperatures kept at 10°C, 20°C, 30°C, 40°C, 60°C, 70°C, 80°C, 90°C and 100°C.
Results
Figure 1: Amount of Copper Precipitated on Glass Vial
Average amount of Copper (g)
1.20
1.00
0.80
0.60
Average Copper (g)
0.40
0.20
0.00
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
Temperature (°C)
Figure 1 shows the amount of copper metal deposited on the inside of the glass vial at
different temperatures. The temperature that produced the most copper (0.98 grams) was
at 53.0°C.
Figure 2: Brilliance of Mirror
Brilliance of Mirror (Scale of 010)
12
10
8
6
Brillianc e of Mirror (Sc ale of 0- 10)
4
2
0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Temperature (°C)
70.0
80.0
90.0
100.0
Figure 2 shows the temperature of the warm water bath vs. the brilliance of the mirror.
The most brilliant mirror was a 10 on our scale and was produced at 53.0°C.
Conclusion
After finding the amount of copper metal produced at varying temperatures ranging from
11.9°C to 98.9°C, we found the most copper produced was at 53.0°C. At 53.0°C, 0.98
grams of copper metal was produced. The 53.0°C trials also had the highest score on our
brilliance test. The quality of the mirrors seemed to decrease at the lower, 11.9°C, and
higher, 98.9°C, temperature extremes. The worst mirror was produced at 11.9°C. This
conformed to our hypothesis by showing that as the temperature increased toward
53.0°C, the quality of the mirror also increased.
As the temperatures increased from 53.0°C to 98.9°C, both the mirror’s brilliance as well
as the amount of copper metal produced decreased, ultimately leading to one of our worst
mirrors at 98.9°C. This contradicted our hypothesis drastically. Instead of the quality
continuing to increase on the interval from 53.0°C to 98.9°C, as it had on the interval
from 11.9°C to 53.0°C, it decreased.
This suggests that above about 50°C, the increasing temperature of the water bath seemed
to hinder the chemical reaction that was taking place. This contradiction to our hypothesis
provokes further study. Testing why 53.0°C produced the best results could include
running experiments on the individual chemicals included in our project to observe how
they behave at different temperatures. The results might explain why the quality
decreased after 53.0°C.
Bibliography
1) Access Science (2002); see http://www.accesscience.com/sci-bin/search
2) Hypertext (2000); see http://www.ucc.ie/ucc/depts/chem/dolchem/html/comp/
nitric.html.
3) Flinn Scientific Inc., (2002). Chem Fax: The Copper Test Tube.
4) BASF Corporation (2003); see
http://www.basf.com/static/OpenMarket/Xcelerate/Preview_cid974236975723_pubid-974236725646_c-Article.html.
5) BASF Corporation (1999); see http://www.basf.com/businesses/
chemicals/intermediates/pdfs/glyoxal.pdf.