• Journal of the Korean Chemical Society
• /
• v.50 no.5
• /
• pp.404-414
• /
• 2006

this study we analyzed and improved an experiment measuring chemical reaction rates introduced in the high school science textbooks through an understanding of the phenomena observed in carrying out the experiment. For this purpose, the contents of textbooks related to the experiment were analyzed, and the problems observed in carrying out the experiment were addressed through experimental analysis. When the experiment was carried out by the method of aquatic transposition presented in textbooks, the observed volume change of H2 gas was delayed and chemical reaction rate was increased in the early stage of reaction period. To resolve these problems, an improved method for measuring the reaction rates was suggested. In the improved experiment the reaction rate was measured to be constant on time, which was interpreted in terms of the concentration of H+ and the surface area of magnesium.

• Journal of the Korean Chemical Society
• /
• v.52 no.3
• /
• pp.303-314
• /
• 2008

The purpose of this study was to understand the experiment for measuring chemical reaction rate by precipitate formation and to develop experiments applying small-scale chemistry. For this study, the experimental method for measuring the effect of concentration and temperature on chemical reaction rates presented in the 10 high school science textbooks were classified by their experimental methods of confirming production. Subsequently, problems observed in carrying out the experiments for measuring chemical reaction rates by precipitate formation frequently presented in the 10 high school science textbooks were analyzed. Experiments applying small-scale chemistry were developed measuring chemical reaction rate by precipitate formation. According to the result of this study, there were some problems in the experimental method of precipitate formation for measuring chemical reaction rates presented in the high school science textbooks. Those problems in the science textbook experiments were insufficient specification of mixing methods of reaction solutions, obscurity of knowing when the character letter X disappeared, time delay in collecting the experimental data, formation of hazardous sulfur dioxide, uneasiness of fixing water bath container, controlling the reaction temperature, and low reproducibility. Those problems were solved by developing experiments applying smallscale chemistry. Presenting the procedure of mixing reaction solutions on the A4 reaction paper sheet made the experimental procedure clearly, using well plates and stem pipette shortened the reaction time and made it possible to continuously collect the experimental data. Furthermore, the quantity of hazardous sulfur dioxide was reduced 1/7 times and the time when the character letter X disappeared could be observed clearly. Since experiments for measuring the effect of concentration and temperature on chemical reaction rates could be performed in 30 minutes, the developing experiments applying SSC would help students understand the scientific concepts on the effect of concentration and temperature on chemical reaction rates with enough time for experimental data analysis and discussion.

• Journal of the Korean Chemical Society
• /
• v.49 no.1
• /
• pp.105-111
• /
• 2005

• Journal of the Korean Chemical Society
• /
• v.37 no.2
• /
• pp.199-205
• /
• 1993

The decomposition of hydrogen peroxide by copper-amines complexes was studied in the pH range of 7.3∼11.3 by measuring the rate of the decreasing concentration of $H_2O_2$. Decomposition rate of hydrogen peroxide increased with increasing pH, and then decreased with increasing pH successively. The mechanism for this type of reaction involves the formation of peroxo complexes in the rate-determining step preceding deprotonation of hydrogen peroxide and copper-amines complexes.

• Journal of the Korean Chemical Society
• /
• v.23 no.6
• /
• pp.396-401
• /
• 1979

Measuring the reaction rate of bilirubin and oxodipyrromethenes with singlet oxygen, we have found oxodipyrromethenes to be better singlet oxygen trapping agents than diphenyl-isobenzofuran, the best such agent known so far. The photooxygenation rates of bilirubin and the model compounds, oxodipyrromethenes approached the diffusion control threshold. A new oxodipyrromethene is synthesized.

• Korean Journal of Materials Research
• /
• v.14 no.6
• /
• pp.407-412
• /
• 2004

Photo decomposition of gas phase benzene by $TiO_2$ thin films chemically deposited on alumina balls were investigated under UV irradiation. Photo decomposition rates were measured in real time during the reaction using a photo ionization detector, which ionizes C-H bonding of benzene molecules and then converts into volatile organic compounds (VOCs) concentrations. From the measuring results, the VOCs concentration increased instantly when IN irradiated because C-H bonds of benzene molecules strongly absorbed on the surface of $TiO_2$ films before the IN irradiation was destroyed by photo decomposition. After that, the VOCs concentration decreased with increasing surface area of $TiO_2$ and reaction time under the IN irradiation. At the optimal conditions for the photo decomposition of gas phase benzene, the reaction rate of the photo decomposition for high concentrations (over 60 ppm) was slow but that of relatively low concentration (under 60 ppm) was fast, due to limited surface area of $TiO_2$ thin films for the reaction. Thus, it is concluded that the photo decomposition rate was mainly affected by the surface area of $TiO_2$ or absorption reaction.

• Journal of the Korean institute of surface engineering
• /
• v.53 no.1
• /
• pp.15-21
• /
• 2020

In this study, growth and burning behavior of 6061 aluminum alloy was studied under constant anodic voltages at various temperatures and magnetic stirring rates in 20% sulfuric acid solution by analysing I-t curves, measuring thickness and hardness of aluminum anodic oxide (AAO) films, observations of surface and cross-sectional images of AAO films. AAO films were grown continuously at lower voltages than 18.5V but burning occurred when a voltage more than 19V was applied in 20% H₂SO₄ solution at 20±0.5℃ and 200 rpm of magnetic stirring. The burning was always related with an extremely large increase of anodic current density with anodizing time, suggesting that high heat generation during anodizing causes deteriorations of AAO films by chemical reaction with acidic solutions. The burning resulted in decreases of film thickness and hardness, surface color brightened and formation of porous defects in the AAO films. The burning voltage was found to decrease with increasing solution temperature and decreasing magnetic stirring rate. The decreased burning voltages seem to be closely related with increased chemical reactions between AAO films and hydrogen ions.

• Applied Chemistry for Engineering
• /
• v.28 no.5
• /
• pp.559-564
• /
• 2017

In this study, the optimization process was carried out by using the central composite model of the response surface methodology in waste cooking oil based biodiesel production process. The acid value, reaction time, reaction temperature, methanol/oil molar ratio, and catalyst amount were selected process variables. The response was evaluated by measuring the FAME content (more than 96.5%) and kinematic viscosity (1.9~5.5 cSt). Through basic experiments, the range of optimum operation variables for the central composite model, such as reaction time, reaction temperature and methanol/oil molar ratio, were set as between 45 and 60 min, between 50 and $60^{\circ}C$, and between 8 and 12, respectively. The optimum operation variables, such as biodiesel production reaction time, temperature, and methanol/oil molar ratio deduced from the central composite model were 55.2 min, $57.5^{\circ}C$, and 10, respectively. With those conditions the results deduced from modeling were as followings: the predicted FAME content of the biodiesel and the kinematic viscosity of 97.5% and 2.40 cSt, respectively. We obtained experimental results with deduced operating variables mentioned above as followings: the FAME content and kinematic viscosity of 97.7% and 2.41 cSt, respectively. Error rates for the FAME content and kinematic viscosity were 0.23 and 0.29%, respectively. Therefore, the low error rate could be obtained when the central composite model among surface reaction methods was applied to the optimized production process of waste cooking oil raw material biodiesel.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.53 no.6
• /
• pp.17-22
• /
• 2011

Biomass gasification provides synthesis gas or syngas that can be used for internal combustion engines as fuel or chemical synthesis as feedstock. Among different types of gasifiers, downdraft gasifier can produce relatively clean syngas with lower tar contents. In this study, a downdraft gasifier was fabricated with 150 mm of hearth diameter to gasify woodchip that is commercially available in this country. After drying woodchip to about 20 %, gasification experiments were conducted measuring temperature, pressure, air and gas flow rates. The volumetric concentrations of CO, $H_2$, $CO_2$, $CH_4$ were 10.7~14.5, 16.5~21.4, 12.5~16.6, and 2.3~2.9, respectively. They were overall within the ranges of the results that the previous studies showed. However, CO concentration was relatively lower and H2 was slightly higher than those from other studies. It seemed that water gas shift reaction was occurred due to the moisture in the fuel woodchip. Additional drying process coupled with syngas cooling would be required to improve the overall efficiency and syngas quality.

• Journal of the Korean institute of surface engineering
• /
• v.32 no.3
• /
• pp.416-422
• /
• 1999

The characteristics of inductively coupled Cl$_2$/BCl$_3$ plasmas during the GaN etching were studied using plasma mass spectrometry by measuring the relative amounts of reactive ions, neutrals, and etch products. GaN etch rates increased with the increase of pressure and showed a maximum near 25mTorr for the pure $Cl_2$ and near 30mTorr for $Cl_2$$BCl_3$. The addition of$ BCl_3$ to $Cl_2$ also was increased GaN etch rates until 50%BCl$_3$ was mixed to $Cl_2$. The GaN etching with pure $Cl Cl_2$ appears to be related to the combination of Cl$_2^{+}$ ion bombardment and the chemical reaction of Cl radicals. In the case of the GaN etching with Cl$_2$/BCl$_3$, in addition to the combined effect of$_2^{ +}$ ions and Cl radicals, $_BCl2^{+ }$ ions appear to be responsible for some of GaN etching even though they do not have significant effect on the GaN etching compared to $Cl_2^{+}$ and Cl. $Ga^{+ }$ , $GaCl^{+}$ , $GaCl_2^{+}$ , and $N_2^{+}$ were observed as the positive ions of etch products, and the intensities of these etch products showed the same trends as those of GaN etch rate. Among the etch products, Ga and $N_2$ appear to be the main etch products.