A student investigates the solubility of three isomeric alcohols—1-propanol, 2-propanol
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A student investigates the solubility of three isomeric alcohols—1-propanol, 2-propanol, and tert-butanol—in water at 25 °C. The student predicts that tert-butanol should be the least soluble because its bulky hydrocarbon portion is most non-polar. However, the measured solubilities (in g solute per 100 g H₂O) are:
• 1-propanol — 100 g
• 2-propanol — 90 g
• tert-butanol — 100 g
Use principles of intermolecular forces to account for the unexpected high solubility of tert-butanol relative to 2-propanol.
(a) Describe the dominant intermolecular interactions between each alcohol and liquid water that govern miscibility.
(b) Explain why increased branching typically decreases solubility of alcohols in water, referring to entropy and enthalpy terms qualitatively.
(c) Provide a molecular-level rationale for why tert-butanol nonetheless exhibits solubility comparable to 1-propanol, despite having the largest non-polar region.
(d) Predict how adding sodium chloride to the water would differentially affect the solubility of the three alcohols, and justify your prediction.