A research team has synthesized a new polar solvent X and wishes to determine its miscibility with commonly used organic liquids. Solvent X has a measured dipole moment of 3.1 D, is capable of forming hydrogen bonds as both donor and acceptor, and has a density of 1.12 g mL⁻¹ at 25 °C.
The team performs preliminary tests by shaking equal volumes of solvent X with each of three reference liquids at 25 °C:
• Liquid P: dichloromethane (CH₂Cl₂), density 1.33 g mL⁻¹, dipole moment 1.14 D, cannot donate hydrogen bonds
• Liquid Q: acetonitrile (CH₃CN), density 0.79 g mL⁻¹, dipole moment 3.9 D, cannot donate hydrogen bonds
• Liquid R: n-hexane (C₆H₁₄), density 0.66 g mL⁻¹, dipole moment 0.00 D, incapable of hydrogen bonding
After equilibration, the observations are as follows:
• Experiment 1 (X + P): single homogeneous phase
• Experiment 2 (X + Q): two liquid layers form
• Experiment 3 (X + R): two liquid layers form
Use these observations to answer the following questions.
(a) For experiments 2 and 3, identify which component (solvent X or the reference liquid) forms the TOP layer. Explain your reasoning based on the data provided.
(b) Propose a coherent explanation, in terms of specific intermolecular forces, for why solvent X is miscible with P but not with Q despite both X and Q possessing large dipole moments.
(c) Design a systematic experimental plan (no advanced instrumentation required) that would allow the research team to quantify the maximum mass percentage of dichloromethane that can be dissolved in solvent X at 25 °C. Include key procedural steps, measurements to be taken, and how the data would be analyzed.
(d) Predict how the addition of a small amount of ethanol to the immiscible mixture of X and n-hexane (experiment 3) might influence the miscibility of the system. Provide a mechanistic rationale involving molecular interactions.