A pharmaceutical researcher is examining the behavior of a small neutral molecule, X
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A pharmaceutical researcher is examining the behavior of a small neutral molecule, X, that contains a single hydroxyl (–OH) group and a short non-polar hydrocarbon chain. The researcher measures qualitative solubility of X in liquid water and in liquid n-hexane at two different temperatures: 5 °C and 37 °C. No numerical solubility data are provided.
Assume that the strength of hydrogen bonding decreases slightly with increasing temperature, whereas dispersion forces are relatively insensitive to this temperature range.
(a) Predict qualitatively how the solubility of X in water will change when the temperature is increased from 5 °C to 37 °C. Provide a molecular-level explanation that incorporates relevant intermolecular forces.
(b) Predict qualitatively how the solubility of X in n-hexane will change over the same temperature range, explaining your reasoning.
(c) Suppose equal masses of X are added separately to water and to n-hexane at 37 °C and the mixtures are allowed to reach equilibrium. If the researcher now combines the two liquid phases in a separatory funnel and shakes the mixture, describe which phase (aqueous or organic) will contain the larger fraction of X after settling. Justify your answer based on polarity considerations and intermolecular interactions.
(d) The researcher plans to modify molecule X by replacing the hydroxyl group with a carboxylic acid (–COOH). Predict how this substitution will affect the distribution of the modified molecule between water and n-hexane at 37 °C, and explain your reasoning in terms of changes to molecular polarity and potential intermolecular forces.