Consider two liquids at 298 K

CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding

Problem

Consider two liquids at 298 K. Liquid X:

M = 32\,\text{g mol}^{-1}

, permanent dipole moment

\mu = 2.6\,\text{D}

Liquid Y:

M = 160\,\text{g mol}^{-1}

, permanent dipole moment

\mu = 0.0\,\text{D}

Based on these data, which statement correctly predicts which liquid will have the stronger net intermolecular attractions and why? (a) Liquid X, because it experiences both dipole–dipole and London dispersion forces, whereas liquid Y experiences only London dispersion forces. (b) Liquid Y, because its greater molar mass leads to a much more polarizable electron cloud, giving London dispersion forces that exceed the combined dipole–dipole and dispersion forces in liquid X. (c) Liquid X, because the strength of dipole–dipole forces rises approximately with

\mu^{2}

, so its large dipole moment makes them far stronger than the dispersion forces acting in liquid Y. (d) Liquid X, because London dispersion forces decrease as molar mass increases, making them weaker in the heavier liquid Y.

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