Using Evaporation to Compare Attraction Between Molecules At the same time, place one drop of each of the liquids on the counter and observe the time it takes for each to evaporate. The liquids are H2O (water), C6H12O6 (oil), and C2H6O (acetone). Indicate the relative time it takes for each to evaporate: fastest, medium, slowest. Letter of Sample: Water, Cooking Oil, Acetone Relative Ranking of Rate of Evaporation Draw the structural formula for the liquids and identify the intermolecular forces present in each liquid. C6H12O6 (oil) C2H6O (acetone) H2O (water) What are the intermolecular forces in each compound (dipole-dipole, hydrogen bonds, dispersion forces)? Which compound has the strongest intermolecular forces? Which compound has the weakest intermolecular forces? What compound with strong intermolecular forces will evaporate quickly or slowly (how easily will it overcome the intermolecular forces between molecules)? Cooking Oil Acetone Water
The Correct Answer and Explanation is:
Relative Ranking of Rate of Evaporation:
- Acetone (C2H6O) – Fastest
- Water (H2O) – Medium
- Cooking Oil (C6H12O6) – Slowest
Structural Formulas and Intermolecular Forces:
- Water (H2O):
Structure:
O
/ \
H H
Intermolecular Forces:- Hydrogen bonding
- Dipole-dipole forces
- Dispersion forces
- Acetone (C2H6O): (propanone)
Structure:
CH3–CO–CH3
Intermolecular Forces:- Dipole-dipole forces
- Dispersion forces
(No hydrogen bonding because there is no hydrogen bonded directly to O, N, or F)
- Cooking Oil (C6H12O6 or similar long-chain molecules):
Structure:
Multiple –OH groups on a carbon chain
Intermolecular Forces:- Dispersion forces (dominant due to large molecular size)
- Some hydrogen bonding (due to –OH groups)
Intermolecular Force Strength Comparison:
- Strongest: Water – because of extensive hydrogen bonding
- Intermediate: Cooking oil – due to large size and dispersion forces, with minor hydrogen bonding
- Weakest: Acetone – no hydrogen bonds, only dipole-dipole and dispersion forces
Evaporation and Intermolecular Forces:
A compound with strong intermolecular forces like water evaporates slowly because more energy is needed to overcome the attractive forces between molecules.
A compound with weak intermolecular forces like acetone evaporates quickly, as less energy is needed to escape into the vapor phase.
Cooking oil has high molecular weight and strong dispersion forces, so it evaporates the slowest.
Conclusion:
- Acetone evaporates fastest due to weak forces
- Water is intermediate due to strong hydrogen bonding
- Cooking oil evaporates slowest due to large size and dispersion forces
