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Introduction

Date: 14/1/2010 Exp. No.: 9 Title: The kinetics of the reaction between iodine and propanone in aqueous solution Aim: The aim of this experiment is to obtain the rate equation for the reaction between iodine and propanone by determining the order of reaction with respect to each reactant and to the catalyst (hydrogen ions). Introduction: The equation of the reaction is: I2(aq) + CH3COCH3 (aq) CH3COCH2I(aq) + H+(aq) + I-(aq) H+ ions acts as a catalyst in this reaction and the rate equation of the reaction is: Rate = k [CH3COCH3]p [I2]q [H+]r The rate equation can be found by varying the concentration of each species in turn while keeping the others constant and follow the reaction using a colorimeter. As the intensity of the iodine colour decreases, more light is transmitted through the solution (i.e. the absorbance decreases). There are three parts to this experiment: 1. Choosing the right filter for the colorimeter. 2. Calibrating the colorimeter so that the meter reading can be converted to concentration of iodine. 3. Obtaining values for the concentration of iodine at intervals of time for a series of experiments with the following sets of conditions: (a) ...read more.

Middle

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Meter reading 0.54 0.48 0.44 0.39 0.35 0.30 0.26 0.21 0.17 0.14 0.12 0.10 [I2(aq)]/ 10-3 mol dm-3 4.0 3.6 3.2 2.9 2.5 2.1 1.8 1.6 1.2 1.0 0.8 0.6 Experiment g Time/min 0.5 1 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Meter reading 0.60 0.57 0.54 0.51 0.48 0.45 0.42 0.39 0.36 0.33 0.30 0.27 [I2(aq)]/ 10-3 mol dm-3 4.5 4.2 4.0 3.8 3.5 3.3 3.1 2.9 2.6 2.4 2.1 1.9 A graph of concentration of I2(aq) against time was plotted for experiment a, f and g (graph 2), and the graphs were attached at the back of the report. Calculation: In graph 2, -Slope = Rate of the reaction -Slope for experiment (a) = = 2�10-4 -Slope for experiment (f) = = 4.2�10-4 -Slope for experiment (g) = = 6.67�10-4 Slope of experiment (f) � 2 � Slope of experiment (a) Slope of experiment (g) � 3 � Slope of experiment (a) For experiment (a), [H+] = 0.4 mol dm-3 For experiment (f), [H+] = 0.8 mol dm-3 For experiment (g), [H+] = 1.2 mol dm-3 Comparing experiments a and f, when the [H+] was doubled, the rate of reaction was around doubled. ...read more.

Conclusion

The use filters prevents light of undesired wavelengths (diffraction of higher order, stray light) from making it to the sample. The light detector measures the amount of light, which passes through the sample. The difference in the amount of monochromatic light transmitted through a colorless sample (blank) and the amount of monochromatic light transmitted through a test sample is a measurement of the amount of monochromatic light absorbed by the sample. Why do we need to draw a calibration curve for each of the colorimeter? This is because each colorimeter is different especially the light source. Light sources in each of the colorimeters give out slightly different amount of light, so we each colorimeter is slightly different and the reading of the same solution may also be different for each colorimeter. Why do we need to use a sample tube to test the sample but not just putting in the whole test tube? This is because the sample tubes are specially designed which their thickness of their glass walls are more even. So that when light pass through the sample tubes, the lights are not affected too much when passing through the glass wall of the sample tube. Reference: http://www.sherwood-scientific.com/chroma/chromaoperation.html http://www.globalw.com/support/colorimeter.html http://www.chemistry-react.org/go/Tutorial/Tutorial_22985.html http://en.wikipedia.org/wiki/Colorimeter_(chemistry) http://www.ehow.com/about_5678160_uses-colorimeter.html http://www.springerlink.com/content/j80460g21468t370/ http://www.multilab.biz/laboratory/colorimeter.htm http://iopscience.iop.org/0022-3735/8/1/016;jsessionid=BDC1E6231798E98A63303AEA73C7323B.c1 http://www.ask.com/questions-about/Colorimeter http://answers.ask.com/Science/Physics/how_does_a_colorimeter_work ?? ?? ?? ?? ...read more.

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