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Optics
Fibroptonic
Ref : 202 012
ENGLISH
2.3 Experiment:
•
Take a glass tank and pour 25 ml of peroxodisulfate solution in it.
•
Prepare 25 ml of potassium iodide in a beaker.
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Place the tank filled with the solution under a light beam; reset the stopwatch.
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Quickly pour the contents of the beaker into the tank and start the stopwatch.
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As the solution becomes brown, the resistance read on the ohmmeter increases.
Note down the times when the resistance passes from one of the values obtained
in the absorption curve of the control solutions earlier.
•
Thus, at these instances the concentration of iodine is well known. Now just plot
the curve of the iodine concentration in function of time. As the iodine ions are
initially in excess, the final iodine concentration tends towards a.
2.4 Note
•
The equation of the reaction is:
•
The temperature is a kinetic factor: the lower it is, the slower the change (try
between 10° and 40°C), even if the critical value "a" is unchanged.
•
We can also study the influence of the initial concentration of iodine or
peroxodisulfate ions.
•
This set-up also helps study kinetics of the reaction between hydrochloric acid
and the thiosulphate ions.
S
or the action of oxalate ions on a potassium permanganate
−
−
2
+ 3
S
2S O
O
2
8
−
2
+
+ 2H
S + SO
O
2
3
73
−
−
2
+
4
3
+ H
O
2
2
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