Effect of Intermolecular Forces on Solubility

Introduction

The purpose of this lab was to explore intermolecular forces and solubility. The first step in achieving this purpose was to complete a variety of chemical reactions between alcohols and solvents and determine which were miscible/immiscible. The next step was to observe capillary action using glass and tygon tubes, with hexane and water. Next we reacted and observed solid iodine and copper sulfate with the solvents hexane and water. 3D models and statistics were created on Spartan of all the molecules we used in this lab, which allowed for greater understanding of what happened during the reactions.

Procedure

Samples of methanol, ethanol, propanol, butanol, and pentanol were all placed in separate vials of H₂O and were observed for reactions and it was decided which of the pairs of substances were miscible together and which were not. With new samples of the same alcohols, the same thing was done with hexane in place of the water. The results were recorded.

Two glass and two tygon tubes were obtained. One of each were individually touched to the surface of a beaker of water, the others touched to the surface of a beaker of hexane. The distance the liquids traveled up the tubing was measured and recorded.

Two vials of each the solutes (water, hexane, and a 50/50 water-hexane mix) were prepared. A piece of Iodine was placed in one of each type of solute, and a piece of copper sulfate was placed in the others. Each mixture was observed, mixed, and observed again. The results were then recorded.

The last part of the lab was using the computer program Spartan to create models of all the alcohol molecules and hexane. The charges of the ions in each molecule, and the dipole moment and direction were found and recorded.

Detailed procedures may be found in reference 1.

1. Results 

Table one shows the data from the solvent and alcohol reactions. The miscible 

(M) combinations were soluble with eachother. The immiscible (IM) combinations were seperated into layers.

Solvent	Alcohol (Solute)
	Methanol	Ethanol	Propanol	Butanol	Pentanol
Water	M	M	M	IM	IM
Hexane	IM	M	M	M	M

Table 1. Solvent and alcohol reaction results.

Table two shows how far the liquids went up the pieces of tubing in the capillary action part of the lab. The water reacted more with the glass than the tygon. The hexane reacted more with the tygon than the glass. 

Liquid	Capillary
	Glass	Tygon
Water	7mm	1mm
Hexane	5mm	14mm

Table 2. Capillary action experiment results. 

Table three shows the results of reacting the solvents with the solids. Both the iodine and the copper sulfate were miscible with water. The iodine was miscible with hexane but turned purple.  The copper sulfate was immiscible in hexane. With the water/hexane mixes had a mix of the results from the other combinations. 

Solvent	Solid
	I2	CuSO4
Water	M	M / dissolved completely
Hexane	M / purple	IM / stuck to sides
Water/Hexane Mix	PS / 1/2 purple, 1/2 NR	1/2 IM / stuck to sides until mixed

Table 3. Results from reacting water, hexane, and a water-hexane mixture, with solid iodine and copper sulfate.  

Discussion

The methanol, ethanol, and propanol have dipole-dipole forces with the water because they are all small polar molecules. Butanol and pentanol are such large molecules that their nonpolar part overpowers their OH^- group so they act like nonpolar molecules and therefore have london dispersion forces. Hexane is a nonpolar molecule so it likes to create london dispersion forces.

Solvent	Alcohol (Solute)
	Methanol	Ethanol	Propanol	Butanol	Pentanol
Water	1. Dipole-Dipole 2. Dipole-Dipole 3. Dipole-Dipole	1. Dipole-Dipole 2. Dipole-Dipole 3. Dipole-Dipole	1. Dipole-Dipole 2. Dipole-Dipole 3. Dipole-Dipole	1. Dipole-Dipole 2. Dipole-Dipole 3. LDF-LDF	1. Dipole-Dipole 2. LDF-LDF 3. LDF-LDF
Hexane	1. LDF-LDF 2. Dipole-Dipole 3. LDF-LDF	1. LDF-LDF 2. Dipole-Dipole 3. LDF-LDF	1. LDF-LDF 2. Dipole-Dipole 3. LDF-LDF	1. LDF-LDF 2. LDF-LDF 3. LDF-LDF	1. LDF-LDF 2. LDF-LDF 3. LDF-LDF

Table 4. The intermolecular forces of the alcohols and solvents. The #1s are the solute/solute forces, the #2s are the solvent/solvent forces, and the #3s are the solvent/solute forces. 

I₂ is a nonploar molecule so it tends to create london dispersion forces. CuSO₄ is a ionic molecule so it tends to create Ion-Dipole forces, which outweigh the other possible forces.

Solvent	Solid
	I2	CuSO4
Water	1. Dipole-Dipole 2. LDF-LDF 3. LDF-LDF	1. Dipole-Dipole 2. Ion-Dipole 3. Ion-Dipole
Hexane	1. LDF-LDF 2. LDF-LDF 3. LDF-LDF	1. LDF-LDF 2. Ion-Dipole 3. Ion-Dipole

Table 5. The intermolecular forces of the solids and solvents. The #1s are the solute/solute forces, the #2s are the solvent/solvent forces, and the #3s are the solvent/solute forces. 

In the capillary experiment of this lab, it was concluded that water reacted more with glass than tygon, and hexane reacted more with tygon than glass. This was because Intermolecular forces bind to similar molecules to one another. The water molecules attract to each other with cohesive forces. Water is polar and glass is also polar so they are attracted to each other with adhesive forces, which are stronger than the cohesive forces and pull the water up the tube. The same goes with hexane-tygon and hexane-glass combinations, but they have stronger cohesive forces. In the water-tygon combinations, the adhesive forces are nonexistent so  there wasn’t enough surface tension and the liquid had nothing to pull it up tube.

Liquid	Capillary
	Glass	Tygon
Water	Adhesive	Cohesive
Hexane	Cohesive	Cohesive

Table 6. Predominate intermolecular forces in the capillary action experiment.

Table seven shows the dipole moment sizes in Debyes, which were found using Spartan. Knowing the dipole moment sizes is useful in determining bond types and forces between molecules.

Molecule	Dipole moment (Debyes)
Water	2.20
Methanol	1.87
Ethanol	1.82
Propanol	1.84
Butanol	1.69
Pentanol	1.62
Hexane	0.00

Table 7. Dipole moment sizes of the molecules used during this lab. 

The dipole followed a trend of decreasing dipole moment size as the molecules got bigger (except for the propanol, which is probably not correct due to an error using the spartan program). This trend was expected, as the OH^-  group has less effect on the polarity on big molecules than small molecules.

References

1. General Chemistry Experiments: A Manual for Chemistry 204, 205, and 206, Department of Chemistry, Southern Oregon University: Ashland, OR, 2009