Lesson 9: 3.9 Separation of Solutions and Mixtures Chromatography
Duration of Days: 1
Lesson Objective
Explain the relationship between the solubility of compounds and the components of a mixture using chromatography or distillation data.
How can we exploit variations in intermolecular forces to separate a homogeneous mixture into its pure components?
What does a high Rf value indicate about a component's relative affinity for the mobile phase versus the stationary phase?
Chromatography
Stationary Phase
Mobile Phase
Retention Factor (Rf)
Distillation
Distillate
Volatility
Learning Objective 3.9.A; Suggested Skill 2.C (Question and Method - Explain experimental procedures).
Covers paper/thin-layer chromatography and distillation. In chromatography, components separate based on their relative attraction to the mobile phase (solvent) versus the stationary phase (paper). In distillation, components separate based on differences in boiling point, which are directly tied to IMF strengths.
When discussing Chromatography and Separation (Topic 3.9), connect it to modern forensic toxicology or anti-doping laboratories. These labs use High-Performance Liquid Chromatography (HPLC) and Gas Chromatography paired with mass spectrometers to separate complex blood or urine samples into individual pure components, identifying prohibited substances or drugs based on their unique interaction signatures with the stationary columns.
Support: Create an analogy grid: Mobile phase = a moving river; Stationary phase = sticky mud on the bank. The component that is more like the river (shares polarities with the solvent) travels the farthest.
Extension: Provide an experimental scenario where a student tries to separate water and ethanol via fractional distillation. Ask them to predict the composition of the distillate at various temperature plateaus.
A student uses paper chromatography to separate a mixture of amino acids. The stationary phase is polar paper, and the mobile phase solvent is nonpolar hexane (C6H14). Component A travels nearly to the solvent front, resulting in a retention factor (Rf) of 0.88. Component B moves very little, yielding an Rf of 0.15. Deduce the relative polarities of Component A and Component B. Justify your answer using intermolecular interactions.