Experiment & Report
EXPERIMENT &
REPORT
Higher Chemistry
CHEMISTRY
Higher (HC)
DISTRIBUTION OF IODINE BETWEEN TWO IMMISCIBLE SOLVENTS
INTRODUCTION
Class practical or Demonstration
Students observe iodine crystals dissolving in equal volumes of two immiscible solvents, aqueous potassium
iodide and cyclohexane, and familiarize themselves with the different colours of the two solutions. To each solution they
add the other solvent, and observe the gradual extraction of the iodine from one layer to the other until an equilibrium
distribution is reached. If the quantity of iodine and the volume of each solvent are the same in both tubes, they should
be able to observe that the same equilibrium position has been reached in both tubes. Using further volumes of the two
solvents, they can demonstrate that it is possible to achieve almost complete extraction from one solvent to the other.
METHOD
1) Select two small crystals of iodine of the same size (do NOT touch the crystals - iodine stains skin and clothes),
and put one into each of two test-tubes.
2) Pour a 2 cm depth of cyclohexane into one test-tube and a 2 cm depth of potassium iodide solution into the
other. Cork the test-tubes and shake until the iodine dissolves. Observe the different colours formed in the two
solvents.
3) Take the tube with the cyclohexane solution, and add an equal volume of potassium iodide solution, without
shaking.
4) Take the tube with the potassium iodide solution, and add an equal volume of cyclohexane, without shaking.
5) Watch for colour developing in the newly added solvent in each tube.
6) Cork both tubes and shake them gently, watching for changes in colour intensity in each tube.
7) Finally shake both tubes vigorously for 15 seconds, allow the two layers to settle out, then compare the colours
in each solvent between both tubes. The situation you should have achieved is called an equilibrium.
8) Use a dropping pipette to remove the bottom layer (coloured potassium iodide solution) from one test-tube, then
add the same volume of fresh potassium iodide solution to the cyclohexane layer and shake.
9) Repeat the removal of the coloured potassium iodide solution and addition of fresh potassium iodide solution
two or three times. What happens to the amount of iodine left in the cyclohexane layer?
10) At the end of the experiment, pour the residues from both tubes into the waste container provided – do NOT
pour down the sink.
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Experiment & Report
Higher Chemistry
Hazards
Wear eye protection.
Cyclohexane, C6H12(l), (HIGHLY FLAMMABLE, HARMFUL, DANGEROUS FOR THE
ENVIRONMENT) - see CLEAPSS Hazcard.
Iodine, I2(s) (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard.
Potassium iodide solution, KI(aq) - see CLEAPSS Hazcard and CLEAPSS Receipe Book.
REPORT
The equilibrium position will be the same whether we start with only the products or only the reactants. This
can be shown in the following experiment.
Iodine is soluble in both water and cyclohexane. Water and cyclohexane do not mix. Iodine sets up an
equilibrium between the 2 layers.
Iodine ( cyclohexane)
⇌
Iodine ( aq)
Draw diagrams to show
Iodine in cyclohexane/ water
iodine(aq) /cyclohexane
equilibrium
 Explain the changes that you see.
 Show on the graph the time at which equilibrium is reached.
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