APEC Youth Scientist Journal Vol.6 / No.2
DETECTING NITRITE DIOXIDE USING COMPLEX
COMPOUND LIGAND SUBSTITUTION
∗
1
Jae Hoon YANG, Won Jung LEE, Ji Yu SEO 1
Changwon Science High School, 30 Pyeongsan-ro 159beon-gil, Uichang-gu, Changwon, Gyeongnam,
KOREA
1. INTRODUCTION
It seems that all people are interested in environmental contamination. When we
watch the news, we can hear a lot of environmental contaminations around the world and the
related environmental disasters. For example, environmental contamination caused by the
exhaust, which contains the hazardous substances such as unburnt HC, SOx, NOx and CO.
Unburnt HC is carcinogenic while SOx and NOx are known to cause acid rain. These
hazardous substances are discharges from the car and NO2, one of the representative
contaminants in exhaust fumes, is the nitrogen oxide surrounding us. Nitrogen oxide is
discharged as exhaust in the high temperatures of the engine. In addition, one of the big
problems these days is the exhaust put into the internal space of the car. Car Performance
Research Center of Korea Transportation Safety Authority tested 5 cars from 3 models of
Grandeur HG manufactured by Hyundai Motors for any infiltration of exhaust gas into the
internal space of the car and Results concluded that exhaust gas was infiltrated into the
internal space of the cars tested. In addition, the same tests were conducted on 13
domestically manufactured cars and 5 imported cars which were manufactured less than 3
years ago. If NO2 is inhaled, it could damage the respiratory system of a human. If highly
exposed to it, people can have pulmonary edema, thus leading to death. In addition, it can
cause bronchial inflammation, asthma, chronic bronchitis and also cough, sputum, tears and
∗
Correspondence to : Jae Hoon YANG ([email protected])
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APEC Youth Scientist Journal Vol.6 / No.2
shortness of breath. In addition, if its concentration is more than 100ppm, it can cause death.
So, NOx is very dangerous and if it enters the passenger space in a car as was discovered in
the recall event, it could endanger our life.
Now in Korea, the chemiluminescence method is used to detect NO2. The
chemiluminescence method measures the volume of light emitted in the range of wave length
of 600~3,000nm to find the concentration of NO in the sample gas. In case of NO2, it shall be
converted to NO using the converter using the thermal dissociation before measuring it.
Detecting NO2 using the chemiluminescence method is time-consuming and expensive.
Accordingly, this team decided to investigate how ordinary people can test NO2. This team
found out about complex compounds while researching on the simple detector such as litmus
testing paper which can detect acidity or basicity. The complex compound is the coordination
compound where a ligand is combined around the metal ion. These complex compounds can
have various colors depending on the ligand which surrounds it. This team has researched the
characteristics of complex compounds and tried to find out how NO2 can be detected using
complex compounds.
2. THEORETICAL BACKGROUND
A complex compound is made up of a coordination compound of metal atom or ion
which can accept one or more electron pairs, and ion and neutral molecules which provide the
electron pair. For examples, in the reaction formula of NH3 + Co3+ -------→ [Co(NH3)6]3+,
4Cl- + Pt3+ -------→ [PtCl4]2-, [Co(NH3)6]3+ is called as complex compound or coordination
compound. When NH3(acting as a Lewis base) approached the Co3+ (Lewis acid), a reaction
occurs. When the transition elements have d orbitals which are completely or partially
vacated, they form complex compounds with the ligands such as H2O, NH3, and Cl- which
provides electron pairs. In [Co(NH3)6]3+, the cobalt ion becomes the central ion while the
ammonia molecule becomes the ligand. The atom which is directly connected to the central
ion in the ligand is called the donor atoms and the number of donor atoms is the coordination
number of the central ions. The most common coordination numbers are 2, 4, and 6.
The combination of complex ions is caused by the electrostatic attraction between
positive charge of the central metal ions and the electrons on the ligand. When ligand
approaches to the central metal ion, the crystal field theory is based on the spatial relation
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between metal ion and ligand in the complex compound and the mutual reaction of
electrostatic attraction and repulsive force. Though in the metal ion, d orbitals has the same
energy, when the ligand having the electron pair approaches, there occurs the repulsive force
between electron of ligand and the d electron of the metal, the energy in the d orbitals is
excited. So, due to the mutual reaction of ligands around the metals and the d orbit of the
transition metal, there occurs the crystal field having the different energy level. If the
approaching ligand electron affects the d orbitals of the metal ion in a completely
symmetrical way, all d orbitals would be excited in the same energy. But if the ligand
approaches x, y and z axis, dz2 orbit and dx2-y2 orbit would be more excited than the
symmetrically formed field due to the repulsive force and 3 orbits such as dxy, dxz, and dyz
would get lower energy than in symmetrical field as it is kept farther away from the ligand.
If energy equivalent to the separation of the crystal field is absorbed, the d orbital
electron in the low energy level will be excited to the high energy level. If the separation of
crystal field is big, the more energy with high vibration is absorbed with the shorter wave
length. The complementary color of the wave length which absorbs the most is absorbed the
least that it can be observed visually when it is infiltrated or reflected.
3. MATERIALS
1. [Co(NH3)5Cl]Cl2 complex solution
98% powered [Co(NH3)5Cl]Cl2 was melted in the distilled water for synthesis.
2. Red Co(OH)2 complex solution
3. Blue Co(OH)2 complex solution
CoCl2 was added to 100ml of 0.1M NaOH solution. Agitate the mixture well for 1 minute. If any blue
sediment is produced, use the filtration to get the sediment. Then, use the distilled water to wash the blue
sediment well. Then, dry the sediment to make the blue Co(OH)2.
4. 97% CoCl2 ⦁ 6H2O, NaOH, HCl, Copper powder, HNO3
The nitrogen dioxide above the inspection criteria was generated by reacting the nitrogen acid solution
with copper.
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4. RESULTS
Experiment 1 – Reaction between [Co(NH3)5Cl]Cl2 and NO2 gas
Figure 1
The reaction of NO2(g) and [Co(NH3)5Cl]Cl2 solution caused the color of solution to
change from red to orange as in Experiment 1. The duration to change to orange was 1 hour
shorter than Experiment 2 and the change in color in the reaction with gas was clearer.
As shown in the table above, as the reaction goes on, the wave length for the most absorption
for the solution was reduced.
Figure 2
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APEC Youth Scientist Journal Vol.6 / No.2
Figure 3
This spectrum is similar to IR spectrum of the experimental result after 2 hours and
30minutes after reaction of Research 1. So, we can understand that the same
[Co(NH3)5NO2]Cl2 is produced in both Research 1 and Research 2. This indicates that even
when NO2 gas is used, the same result is acquires as in Research 1.
Experiment 2 - Reaction of Co(OH)2 solution and NO2
First of all, we found out that the reaction of red Co(OH)2 solution and NO2(g) would
make the pink Co(OH)2 solution change to red. It took almost 3 minutes for the color of
solution to change, showing that it is better suited to detect the NO2 compared with the
[Co(NH3)5NO2]Cl2 solution.
We found out that the reaction of synthesized blue Co(OH)2 solution of NO2(g) changed the
color from blue to red. It took almost 2 minutes for the color of solution to change, showing
that it is better suited to detect the NO2 compared with the [Co(NH3)5NO2]Cl2 solution.
The actual maximum absorption wave length was measured by using UV-Vis. After
reaction, the maximum absorption wave length of blue Co(OH)2 solution was 510nm while
that of red Co(OH)2 was 511nm.
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APEC Youth Scientist Journal Vol.6 / No.2
Figure 4
Figure 5
Figure 6
Figure 7
Table 1
Before reacting Red
Co(OH)2 complex solution
After reacting Red
Co(OH)2 complex solution
Before reacting Blue
Co(OH)2 complex solution
After reacting Blue Co(OH)2
complex solution
Maximum absorption
wave length(nm)
Abs
x
x
511.00
0.374
x
x
510.00
0.173
Figure 8
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APEC Youth Scientist Journal Vol.6 / No.2
The IR analysis results showed that the substance was inorganic nitrate. In addition,
as the peak of N-O bonding appeared 1600cm-1, the substance is likely to be Co(NO3)2. But
further confirmation is required.
Experiment 3 - Test of recycling of Co(OH)2
Figure 9
Figure 10
We put Co(NO3)2 generated in Research 3 into NaOH solution for reaction. Then, the
color of solution turned blue.
5. CONCLUSION
Experiment 1 - Reaction between [Co(NH3)5Cl]Cl2 solution and NO2
The experiment showed that the color changes when there is the reaction between
NO2 gas and [Co(NH3)5Cl]Cl2 solution, showing that NO2 can be detected when the ligand
replacement is used for the complex compound. It also showed that when the solution reacts
with the gas, the color changed faster and clearer than the reaction with NaNO2.
Figure 11
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APEC Youth Scientist Journal Vol.6 / No.2
The graphs above show the solutions taken after 30 minutes, 1 hour, 1 hour and 30
minutes, 2 hours and 2hours and 30 minutes after reaction from above.
The measurement of the actual longest light absorption wave length using the UV-Vis
showed that depending on the concentration of NO2, the longest light absorption gets shorter.
As the fact that the longest light absorption wavelength gets shorter means that big energy
light is absorbed, it means that the Cl- replaces the NO2- of the relatively strong long ligand to
become [Co(NH3)5Cl]Cl2, confirming that it is actually the red solution.
Experiment 2 - Reaction of Co(OH)2 solution and NO2
In this experiment, it was found out that when there is a reaction between NO2 gas and
Co(OH)2 solution, there is a change in color. As the color of solution changes from blue to
red, the change of color was easier to find than in case of the solution of [Co(NH3)5Cl]Cl2.
Also as it only took 2 minutes for Co(OH)2 solution to change color, it was more appropriate
to use as a simple detector than [Co(NH3)5Cl]Cl2 which took one hour.
In addition, the UV-Vis measuring showed that the strong and long ligand of NO3- acted as
ligand and thus the crystal field splitting energy increased, thus producing the red product by
absorbing the short wave length.
Experiment 3 - Test for reusing Co(OH)2
Co(OH)2 which were used to detect NO2 was synthesized again. This showed that the
solution which was used for detection can be reused. If the solution is reused, the cost for
detecting NO2 can be reduced, compared with the conventional method.
6. ACKNOWLEDGEMENT
We would like to thank Mr. Jo Jin-Woo for his support for leading our experiments to
success. In addition, we also express gratitude Mr. Kang Dae-ha, Principal and Department of
Chemistry of Changwon Science High School for providing us materials and apparatus
required for the experiments.
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7. REFERENCES
[1] Octahedral iron(II) phthalocyanine complexes: multinuclear NMR and relevance as NO2
chemical sensors Pascual O˜na-Burgos,a Mar´ıa Casimiro,a Ignacio Fern´andez,*a Angel
Valero Navarro,b Jorge F. Fern´andez S´anchez,*b Antonio Segura Carreterob and Alberto
Fern´andez Guti´errezb
[2] NICKEL PHTHALOCYANINE BASED NITROGEN DIOXIDE GAS SENSOR, Datir
A.M., Ghole V. S.1 and Chakane S. D.*2
[3] TRANSITION METAL NITRITE COMPLEXES, MICHAEL A. HITCHMAN and
GRAHAM L. ROWBOTTOM
Jae Hoon YANG
Won Jung LEE
Ji Yu SEO
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