Explain why a) Kl (potassium iodide) dissolves in water, but b) it will not dissolve in
hexane.

Explanation: Brief description of demonstration

Three clear liquids form three distinct layers in a cylinder. Iodine crystals sprinkled on the top layer sink and form pink solutions with the top and bottom layers but do not dissolve in the middle. When the liquids are mixed, two layers form: a pink layer on the bottom, and a colorless layer on top. When white potassium iodide crystals are added and the liquids are mixed again, the colorless layer turns yellow.

Concepts illustrated:

• Phases and phase boundaries (surfaces)

• Density

• Polar/non-polar (hydrophilic/hydrophobic) interactions

• Solubility, miscibility

• Chemical reaction

• Extraction

• [Solution and emulsion]

Materials

• Clear glass reaction cylinder or gas-washing bottle, at least 200 mm tall, with ground glass stopper (A cylindrical container is preferable to a separatory funnel for this experiment. The stopper must be non- reactive, and, to prevent a potentially dangerous pressure build-up, the stopper must be easily released. For a very small class, a large test tube with a suitable stopper is adequate. )

• Equal volumes of chloroform, water, and hexane (The volume of each liquid should be a little more than one-fourth the volume of the cylinder.)

• Iodine crystals and small spatula

• Potassium iodide crystals and medium spatula

Preparation

Work in a hood. Pour the chloroform into the reaction cylinder. Add the water and allow the liquids to separate completely. (If necessary, speed the process by holding the cylinder vertical and gently swirling the solution with a circular motion.) Tip the cylinder and pour the hexane slowly down the side to prevent mixing. Close the cylinder and set it aside, away from sources of heat, until time for the demonstration.

It forms single phase mixtures (solutions) with other polar and ionic substances. ... Since water is less dense than this non-polar mixture, the bubbles rise to the top. Potassium iodide, an ionic compound, dissolves easily in water but does not dissolve in chloroform and hexane.

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