Purpose/Goal:
A demonstration showing the miscibilities of solid iodine, cyclohexane, water and carbon tetrachloride as well as characteristic relative solvent densities.
Explanation of Experiment:
Iodine is a purple solid and sublimes when allowed to stand in an open container at room temperature. Cyclohexane is a nonpolar colorless organic liquid with formula C6H12. Water is a colorless polar liquid with formula H2O. Carbon tetrachloride is a nonpolar colorless organic liquid with formula CCl4. When the lecturer tries to dissolve iodine in water, a slight solubility is noted by the slight discoloration of the liquid. The presenter then places solid iodine in cyclohexane – solid dissolves as noted by the intense purple translucent color of the resulting solution. He then places carbon tetrachloride in a large test tube and introduces solid iodine, resulting in another dissolution as noted by the intense purple translucent color of the resulting solution. The water/iodine supernatant is then carefully poured into the test tube. Water is not miscible with carbon tetrachloride because of their differing polar characteristics. Note the two distinct layers. This is because of the liquids’ differing densities. The cyclohexane solution is then carefully introduced into the test tube – note that a third layer is now formed in the tube. The test tube is corked and shaken. What happens? The result is two layers of liquid. Since the cyclohexane and carbon tetrachloride are both nonpolar liquids and are miscible with each other, they form a homogeneous solution in the lower part of the test tube. The polar water solution is now the upper layer of liquid in the tube. Note that, interestingly, if enough cyclohexane was introduced into this system, the average density of the resulting nonpolar solution can be adjusted so that the nonpolar solution ends up on top of the water instead of below it.
