A chemistry student is comparing three molecular substances that are all solids at –20 °C. Relevant data are provided in the table.
Substance Molar Mass (g mol−1) Dipole Moment (D) Normal Melting Point (°C)
A (acetic acid) 60 1.7 16
B (ethanol) 46 1.7 –114
C (butanone) 72 2.8 –86
(1) Rank substances A, B, and C in order of increasing strength of intermolecular forces present in their molecular solids at –20 °C. Justify your ranking by referring explicitly to both the numerical data in the table and the molecular structures of the substances.
(2) Identify which of the three substances are capable of forming hydrogen bonds in the solid state. Explain how the information in the table supports your identification.
(3) Predict the order of vapor pressures of the three substances at 20 °C (highest to lowest) and provide reasoning that links vapor pressure to intermolecular forces.