Methanol (CH3OH) and methane (CH4) each contain one carbon atom, yet their macroscopic properties differ markedly. Selected data are provided below.
Substance
Molar mass (g mol−1)
Normal boiling point (°C)
Dynamic viscosity at 25 °C (mPa·s)
Methanol
32
65
0.59
Methane
16
–164
0.012
Answer the following with respect to the particulate-level interactions present in each substance.
(a) Identify all types of intermolecular forces that exist between molecules in liquid methanol and in liquid methane.
(b) Using the information in the table and your answer to part (a), explain the large difference in the normal boiling points of the two substances.
(c) At 25 °C, which substance has the higher vapor pressure? Justify your answer in terms of intermolecular forces and kinetic considerations.
(d) Methanol forms droplets with noticeably greater contact angles on clean Teflon® than on clean glass. Explain this observation in terms of the intermolecular interactions between methanol and each surface.