SCH4C           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.
    In this experiment you will determine the solubility of a polar solute (glycerol), a non-polar solute (iodine), and an ionic solute (sodium chloride) in three different solvents: water, ethanol, and dichloromethane.  Water is a highly polar solvent, ethanol is moderately polar, and dichloromethane is non-polar.

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

Procedure:
1.    Prepare a data table that will allow you to record your obsersvations for each solute-solvent combination.
 

Solvent \ Solute 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.

Questions:
1.    In what solvent is glycerol most soluble? In what solvent is it the least soluble?

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?