Purpose:To study temperature

Materials:

Safety:

Pre-Lab Exercise:

Substance FormulaStructural Formula

Molecular Weight

Hydrogen Bond

Ethanol C2H5OH 46 g/mol Yes

1-propanol C3H7OH 60 g/mol Yes

1-butanol C4H9OH 74 g/mol Yes

N-pentane C5H12 72 g/mol No

Methanol CH3OH 32 g/mol Yes

N-hexane C6H14 86 g/mol No

Procedure:

Data Tables:

Substance t1 (oC) t2 (oC) Δt (t1-t2) (oC)Ethanol 23.62 12.44 11.18

1-propanol 22.38 13.37 9.011-butanol 23.50 21.24 2.26

N-pentane 21.99 10.00 11.99Methanol 23.22 9.08 14.14N-hexane 24.27 11.20 13.07

Substance Predicted Δt (oC) Explanation

1-butanol Lower than propanol

The more hydrogen present and the higher the molecular weight of a substance, the higher the intermolecular forces should be. Therefore, less butanol than propanol should evaporate, thereby decreasing the temperature less, resulting in a lower Δt.

N-pentaneHigher than butanol

and hexane

Pentane is roughly the same molecular weight as butanol. Therefore, the only difference in their intermolecular forces is due to hydrogen bonding, and lack thereof. Since it lacks hydrogen bonds, pentane should therefore have weaker intermolecular forces than butanol, resulting in a higher Δt. Also, hexane also lacks hydrogen bonding, but has a higher molecular weight than pentane, so pentane should have a higher Δt that it as well.

Methanol Higher than ethanol

The less hydrogen present and the lower the molecular weight of a substance, the higher the intermolecular forces should be. Therefore, more methanol than ethanol should evaporate, thereby decreasing the temperature more, resulting in a higher Δt.

N-hexane Lower than propanol

Hexane and propane both lack hydrogen bonding, but hexane has a higher molecular weight than pentane, so it should have a lower Δt that pentane.

Processing the Data:1. N-pentane and 1-butanol are about the same

molecular weight and of very similar molecular structures, so any difference in the strength of their intermolecular forces must come from the fact that pentane lacks hydrogen bonding, while butanol has hydrogen bonding. The stronger a substance’s intermolecular forces, the less will evaporate, and so the less the temperature will change; and vice-versa. This explains the difference between the Δt’s.

2. As said above, the stronger a substance’s intermolecular forces, the less will evaporate, and so the less the temperature will change; and vice-versa. Therefore, the alcohol with the lowest Δt must have the strongest intermolecular forces, and the one with the highest Δt must have the weakest intermolecular forces, so 1-butanol has the strongest intermolecular forces of attraction and methanol has the weakest.

3. As said above, the stronger a substance’s intermolecular forces, the less will evaporate, and so the less the temperature will change; and vice-versa. Therefore, the alkane with the lower Δt must have the stronger intermolecular forces, and the one with the higher Δt must have the weaker intermolecular forces, so n-pentane has the stronger intermolecular forces of attraction and n-hexane has the weaker.