A research team is studying the environmental fate of a spill consisting of equal…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A research team is studying the environmental fate of a spill consisting of equal volumes of four immiscible or partially miscible liquids poured simultaneously into a deep, quiescent freshwater pond. The liquids, listed alphabetically with their densities and dominant intermolecular forces, are as follows:
• Bromobenzene (ρ=1.49gmL−1, nonpolar, London dispersion)
• Castor oil (ρ=0.96gmL−1, largely nonpolar but high viscosity)
• Ethylene glycol (ρ=1.11gmL−1, highly polar, extensive hydrogen bonding)
• Hexanes (ρ=0.66gmL−1, nonpolar)
Assume water in the pond has density 1.00gmL−1 and that temperature remains uniform. No chemical reactions occur.
(a) Predict the complete vertical ordering of all phases (including water) that will exist long after the spill, beginning with the topmost phase and ending with the bottommost. State whether each phase is pure or a mixture, and if a mixture identify its main components.
(b) Discuss how the viscosity of castor oil might slow—but not ultimately prevent—the establishment of the equilibrium layering you proposed in part (a). In your answer, relate viscosity to molecular structure and to the timescale of phase separation.
(c) The team obtains water samples at several depths and detects low but measurable concentrations of bromobenzene well below its designated phase boundary. Provide a mechanistic explanation for how bromobenzene molecules could be present in these deeper water samples despite bromobenzene’s immiscibility with water.
(d) Suppose winter brings a uniform temperature drop that increases the density of water to 1.02gmL−1 and increases the viscosity of castor oil. Evaluate qualitatively whether any changes in the layer ordering from part (a) are expected. Justify your answer with reference to both density and miscibility considerations.