Distribution equilibrium

Principle

At constant temperature and under constant pressure, a dissolved substance distributes itself between two immiscible liquids in a constant concentration ratio. This ratio is equal to the partition coefficient (distribution coefficient) of the substance examined in the given two-phase system.

Benefits

• Modern, easy-to-use photospectrometer

Tasks

1. Measure the extinction of various concentrated solutions of trans-azobenzene in acetonitrile at constant wavelength. Subsequently determine the equilibrium concentrations (extinctions) of trans-azobenzene in the system n-heptane / acetonitrile after single and repeated distribution at constant temperature.
2. Calculate the partition coefficients and effectiveness of the extractions from the experimental data and compare them.

Learning objectives

• Principles of thermodynamics
• Partial molar free enthalpy (chemical potential)
• Equilibrium between phases
• Distribution and extraction
• Nernst distribution equation
• Lambert-Beer law
• Photometry

Necessary accessories

• Precision balance 620g/0.001g