Lab #6 - Molecular Polarity and Solubility
Introduction: You are aware that
sugar dissolves in water but oil does not. What factors determine whether
one substance will dissolve in another? For a solute to dissolve
in a solvent, the solvent particles must be able to overcome the attractive
forces between the solvent particles and create a space for themselves.
Also, the solute particles must be able to overcome the attractive forces
holding them together. If the attractive forces between solute particles
and solvent particles are sufficiently strong, enough energy is released to
overcome the attractive forces within the solute and the solvent and dissolving
occurs. Solubility then, depends in part on the nature of the solute
and the nature of the solvent.
Problem: How does the nature of the solute and the nature of the solvent affect solubility?
Apparatus: Test tubes, rubber stoppers, test tube rack
Materials: glycerol, iodine, sodium chloride, distilled water, ethanol, dichloromethane
2. Place 5 mL of water in each of three test tubes. Add 1 mL of glycerol to the first test tube, two small iodine crystals to the second and a few small sodium crystals to the third. (CAUTION: Do not touch the iodine crystals!) Stopper all three test tubes, shake them vigorously, and allow them to stand for 1 minute. Observe the contents of each test tube and record your observations.
3. Repeat Step 2 using ethanol instead of water.
4. Repeat Step 2 using dichloromethane instead of water.
2. In general, in what type of solvent (non-polar, moderately polar, or highly polar) are polar solutes most soluble? Explain why.
3. In what solvent is iodine the most soluble? In what solvent is it the least soluble?