Page 15 - Lab Manual & Project class 12

CHEMICAL KINETICS

(iii) Why does iodine impart blue colour to starch?
(iv) Explore the possibility of using an oxidant other than H O in this experiment.
2 2
(v) Why is the reaction given the name clock reaction?
(vi) Why should the concentration of sodium thiosulphate solution taken be always less than
that of potassium iodide solution?

EXPERIMENT 2.3

Aim

To study the rate of reaction between potassium iodate (KIO ) and
3
sodium sulphite (Na SO ).
2 3

Theory

The reaction between KIO and Na SO indirectly involves the
3 2 3
formation of iodide ions, which are oxidised in acidic medium by
–
IO ions to iodine. The overall reaction proceeds in the following
3
two steps. Maxbrain Chemistry
2–
–
–
IO + 3SO → I + 3SO 2– (1)
3 3 4
–
+
–
5I + 6H + IO → 3H O + 3I (2)
3 2 2
The evolved iodine produces blue colour with the starch
solution in a manner described in the previous experiment.
This reaction like the earlier reaction is also known as ‘clock
reaction’.

Material Required

• 2 M Sulphuric acid : As per requirement
• Conical flasks (250 mL) : Six • 5% Starch solution : As per requirement
• Measuring
• 6% Potassium iodate
cylinder (100 mL) : One solution : As per requirement
• Stopwatch : One
• 6% Sodium sulphite
• Trough : One
solution : As per requirement

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24-04-2018