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CONTRIBUTORS:
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CONFERENCE NAME:
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CONF. LOCATION:
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Plovdiv, Bulgaria
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CONFERENCE YEAR:
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2007
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PUB TYPE:
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Conference Presentation
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SUBJECT(S):
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chemistry - computational; chemistry - inorganic; chemistry - physical; informatics - applied; mathematics - analysis; mathematics - applied; mathematics - modeling; mathematics - optimization; mathematics - statistics; physics - optics; research - methodology
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DISCIPLINE:
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Chemistry
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HTTP:
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http://lori.academicdirect.org/works/?id=125
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LANGUAGE:
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English
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PUB ID:
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103-436-075
(Last edited on
2007/07/08 09:44:10 GMT-6)
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SPONSOR(S):
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ABSTRACT:
Introduction
The kinetics study of the reaction between Cu2+ and S2O32- in solutions is not entirely studied, being reported into the specialty literature just few papers which refer the reaction in aqueous solutions.
Aim
By using of a set of experimental data obtained from stopped flow spectrophotometrical installation build at Technical University of Cluj-Napoca, to investigate the kinetic of the reaction.
Assumption
The general form of the reaction is A + B <=> X -> P
Experimental procedure
The cooper and tiosulfate aqueous solutions were prepared in different concentrations varying from 0.001 M to 0.01 M. The reaction was detected to be a very fast one: the existence of the X intermediary was found to be below 25 ms. The wavelength of light detection diode was found (and is 430 nm) in order to prepare the detection of intermediary forming as the wavelength which assures the best stability of the light emission in time. A microampere meter was set in order to be used for recording of the signal from detector and the baud rate of the recording was choused to be 0.04 ms. A digital oscilloscope with buffer was used to plot and transfer the data to the computer. In order to minimize the experimental interferences such as dilution of the intermediary, the size of the mixing chamber was varied; a small size one was selected and used for measurements. The mixing chamber has a volume equal to 0.35cm3 and the length of optical pathway traversed by the beam through measurement chamber is 0.4 cm.
Experiments
Three experiments with equal concentration of reactants (0.001, 0.005 and 0.01 M) are the subject of this investigation. The recording of digital data was started always after the mixing moment but near to, because of limited memory buffer of the oscilloscope (64 Kb). The number of relevant measurements corresponding to the reaction time it varies in 1500-8000 range.
Mathematical Methods
The Lambert-Beer law was used to correlate extinction with concentration; the unknown parameter was the molar extinction coefficient. The mathematical model of the assumed reaction mechanism was numerically written; the unknown parameters were four partial reaction orders and three reaction rates constants. The subject of optimization was squared sum of differences between experimental extinction E and theoretical approach of extinction a[X]. Only a first part of the experimental data records entered into the optimization procedure (1100 for 0.001 M, 1300 for 0.005 M, and 6500 for 0.01M).
Results
The optimization procedure produced the best fit of the model to the experiment with 0.962, 0.955, and 0.980 respectively correlation coefficients. Not all unknown parameters were possible to be obtained. Reaction rates: only to the right ones. Partial orders: all, except one of intermediary for the left direction reaction. Extinction coefficient: 212 +/- 22 1/mol*cm. For all obtained parameters is no significant difference between parameters values from one experiment to another with a 95% confidence.
Conclusion
Reaction kinetics was almost complete determined. Reaction rates: 2000 +/- 1000, N/A, 2200 +/- 200, partial orders: 0.789 +/- 0.05, 0.781 +/- 0.04, N/A, 1.55 +/- 0.04. The optimization procedure was proved to be a self consistent one, despite of the number of unknown parameters used.
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