A chemist is studying the miscibility behavior of a ternary liquid mixture composed…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A chemist is studying the miscibility behavior of a ternary liquid mixture composed of acetone (CH₃COCH₃), water (H₂O), and 1-octanol (CH₃(CH₂)₆CH₂OH) at 25 °C. The chemist mixes equal volumes (5.0 mL each) of the three liquids, shakes the mixture vigorously, and allows it to stand until equilibrium is reached. Two immiscible layers are observed.
Consider the following additional data:
• Acetone–water: completely miscible at 25 °C
• Acetone–1-octanol: partially miscible; at most 12 % by mass of acetone dissolves in 1-octanol at 25 °C
• Water–1-octanol: solubility of 1-octanol in water is 0.0003 mol per mol H₂O at 25 °C
Answer the questions below.
(a) Identify all pairs of the three liquids that are mutually miscible in significant proportions at 25 °C. Support your answer with reasoning based on molecular structure and intermolecular forces.
(b) After phase separation, which component (acetone, water, or 1-octanol) do you expect to be present in greatest mole fraction in the TOP layer? Justify your answer using both density considerations (water: 1.00 g mL⁻¹; acetone: 0.79 g mL⁻¹; 1-octanol: 0.83 g mL⁻¹) and intermolecular interactions.
(c) The chemist repeats the experiment at 55 °C. Predict qualitatively how the composition of each layer will change compared with the composition at 25 °C. Provide a molecular explanation that refers to temperature effects on intermolecular forces.
(d) Design an additional simple experiment (no specialized instrumentation) that would allow the chemist to quantify the amount of acetone present in the 1-octanol–rich layer after separation at 25 °C. Outline the procedure and explain how the data collected would be used to determine the desired quantity.