Intermolecular Forces-The Relationships Between Physical Properties and Structure

Data and Observations

Part A: Table 1

Part B: Table 2

Part C: Table 3

M= Miscible I= Immiscible

*Note: The results in this table above the X's were predictions done before the experiment. The actual results after experimentation are show below the X's

Part D: Table 4

S= Soluble I= Insoluble

Results & Discussion

Part A

In Run 1 of volatility, including pentane, heptane, and decane, the pentane was observed as being the most volatile and the decane was observed as being the least volatile. The dispersion forces between the smaller pentane molecules are much weaker than the forces between the larger decane molecules. Therefore, pentane as the largest vapor pressure and decane the smallest. Run 2 consisted of comparing methanol butanol and ethanol. It was discovered that methanol was the most volatile and butanol was the least volatile. All of these molecules have hydrogen bonding and dispersion forces present. Methanol and ethanol also have dipole-dipole forces. The quickness of evaporation in this run depended greatly on the molecular mass of the molecules. Methanol being the lightest in molecular mass, evaporated more quickly than ethanol and butanol. In Run 3 of Part A pentane, butanol, and deionized water were tested for volatility. Because pentane has the weakest intermolecular forces-dispersion forces, it was the first to evaporate. The deionized water was the least volatile, this is because the hydrogen bonding between water is a lot stronger than the hydrogen bonding of the butanol which was observed to have an intermediate volatility.

Part B

By gently rolling and swirling three test tubes containing hexane, glycerol, and deionized water, we observed which of the liquids had the highest viscosity at two different temperatures. Shown in Table 2 are the results. When we tested the viscosities after being heated, there was a distinct difference in the viscosities. As the temperature of the liquids were increased, the viscosity decreased. As more energy was added, the molecules within the liquids began to move around more, making them more farther apart from one another. Hexane having only dispersion forces, which are the weakest of all, makes it least viscous. Glycerol has three OH bonds, making it the strongest out of the three molecules being tested. Increases in the attractive forces between molecules increases the resistance to flow.

Part C

The majority of the molecules being tested for miscibility have hydrogen bonding. Referring to Table 3, ethanol and H₂O were observed as being miscible. The rule of thumb with determining miscibility is "like dissolves like". This means that liquids with similar molecular structures and similar polarity with likely dissolve in each other. The "like dissolves like" rule is also apparent when you try to mix hexane and H₂O. Hexane contains no polar groups within its structure, making it immiscible with water. When a substance is immiscible, there are two distinct phases left in the test tube.

Part D

As in Part C where "like dissolves like," that is also the key for Part D in determining the solubilities. Referring to Table 4, it is apparent that H₂O, which is polar, would dissolve KMnO₄ which is also polar. Polar solvents dissolves polar solutes and non-polar solvents dissolve non-polar solutes. Ionic solutes will dissolve in polar solvents because the positive ion is attracted to the partially negative charged atom in the polar solvent molecule.

Questions

1. CaCl₂ would be more soluble in methanol. Since CaCl₂ has polar bonds, it is more likely to dissolve in a polar solvent like methanol.

2. First, it would be easiest to separate the NaCl from the mixture by using water to filter it out. The salt will dissolve and leave the sand behind. With the remains of the filtration, why evaporating the water from the salt solution will result in only salt. Keeping in mind that like dissolves like, to separate the iodine and n-pentane, and ionic substance could be added to filter the iodine out of the mixture.

3. The end that is soluble with H₂O is the end with O₂ on it. The end that is soluble with n-hexane would be the end of the molecule with CH₃ (non-polar).

5. Possible isomers for C₂H₆O would be ethanol and dimethyl ether. The boiling point of ethanol is 78.4 ºC and the boiling point of dimethyl ether is -23.6 ºC. The reason the ethanol has a higher boiling point is because of the stronger intermolecular forces present in the molecule. Ethanol has hydrogen bonding, dipole-dipole, and dispersion forces, while dimethyl ether has only dispersion forces.

Conclusion

It is clear that after completing this experiment that physical properties such as viscosity, solubility, and volatility all effect the intermolecular forces in a molecule.