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Optics
Fibroptonic
Ref : 202 012
1 Purpose
To study the kinetics of the chemical reaction between potassium iodide and sodium
peroxodisulfate solutions using photometric measurements.
2 Experiment no. 25
ENGLISH
FIBROPTONIC
2.1 Equipment:
•
Photoresistor module
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Ohmmeter
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Directive white light source or laser
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Set of identical glass tanks
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Potassium iodide solution of 0.5 mol/litre
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Sodium peroxodisulfate solution of 0.05 mol/litre.
•
Stopwatch
2.2 Set-up:
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Mix 250 ml of potassium iodide with 250 ml of sodium peroxodisulfate, the
solution becomes yellow and then slowly turns brown with the formation of iodine
(I3 ions). Wait for about one hour (this depends on the ambient temperature). The
solution obtained does not change anymore. We now prepare different control
solutions of known concentration by dilutions: a – 0.8 a – 0.6 a – 0.4 a –0.2 a –
0.1 a – 0.05 a – 0.025 a etc. (a is the concentration of I3 ions in the solution
obtained earlier, that is 0.025 mol/litre. The volume of each solution is 50 ml.
•
Connect the ohmmeter to the black and yellow terminals of the photoresistor
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Illuminate the photoresistor by the light beam (adjust the distance between the
source and the photoresistor in such a way that the lighted area is not too small).
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Introduce the tank containing the control solution in the beam, for example one
with a concentration of: a = 0.025 mol/l (refer to figure 28); measure the value of
the resistance R of the photoresistor.
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Restart the operation with each of the control solutions by checking that there is
no change in the relative arrangement of the beam, the tank or the photoresistor.
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Plot the curve representing R in function of the iodine concentration.
CHEMICAL KINETICS
72
SHEET
13
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