CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Acetic acid, CH₃COOH, is a molecular solute that can interact with solvents through multiple intermolecular forces. Three separate, sealed vials are prepared at the same temperature, each containing a small amount of liquid acetic acid thoroughly mixed with an equal volume of one of the following pure solvents:
• Water (H₂O)
• Methanol (CH₃OH)
• n-Hexane (C₆H₁₄)
After mixing and settling, you observe complete miscibility in some vials and phase separation in others.
(a) For each solvent, identify every site on the acetic acid molecule that can serve as a hydrogen-bond donor or acceptor. Then state which of those interactions each solvent is capable of forming with acetic acid.
(b) Rank the three solvents from greatest to least expected solubility of acetic acid. Provide a clear justification based on the number and strength of possible solvent–solute intermolecular interactions.
(c) In the vial where phase separation is expected, describe the orientation of acetic acid molecules at the interface between the two layers. Explain how this orientation minimizes the system’s overall potential energy.
(d) Propose a structural modification to acetic acid that would significantly increase its solubility in n-hexane without greatly decreasing its solubility in methanol. Justify your proposal in terms of intermolecular forces and molecular polarity.