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.


  • Modern, easy-to-use photospectrometer


  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.

What you can learn about

  • 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


Scope of Supply
Device NameItem no.Qty
Converter USB - RS232, active14602-101,00
Erlenmeyer flask,Duran®, narrow neck, 250 ml36124-001,00
Erlenmeyer flask, Duran®, narrow neck, 500 ml36121-001,00
Trans-azobenzene f. synth., 25 g31064-101,00
Spectrophotometer WPA S800+, 325...1100 nm35603-991,00
Cell for spectrophotometer, optical glass35664-002,00
Weighing dishes, square shape, 84 x 84 x 24 mm, 25 pcs.45019-251,00
Microspoon, steel33393-001,00
Erlenmeyer flask, Duran®, narrow neck,1000 ml36122-001,00
Erlenmeyer flask, Borosilicate, narrow neck, 500 ml46143-001,00
Erlenmeyer flask, borosilicate, narrow neck, 250 ml46142-001,00
Rubber stopper,d=44/36mm,w/o hole39262-001,00
Rubber stopper, d = 35 / 29 mm, without hole39259-002,00
Volumetric flask, Borosilicate, 50 ml, IGJ12/2136547-004,00
Volumetric flask 250 ml, IGJ14/2336550-001,00
Funnel, glass, top dia. 50 mm34457-001,00
Retort stand, h = 750 mm37694-001,00
Support ring, i.d. 70mm,37721-012,00
Right angle boss-head clamp37697-002,00
Separatory funnel 250 ml pear-sh.36884-004,00
Separatory funnel 1000 ml35850-041,00
Volumetric pipette, 10 ml36578-001,00
Volumetric pipette, 20 ml36579-002,00
Pipette dish36589-001,00
Beaker, Borosilicate, tall form, 100 ml46026-002,00
Pasteur pipettes, 250 pcs36590-001,00
Rubber caps, 10 pcs39275-031,00
Thermometer -10...+50 °C38034-001,00
Wash bottle, plastic, 500 ml33931-001,00
Acetonitrile 100030000-701,00
n-heptane, extra pure 25031366-251,00

Downloads and Documents

Document  Filesize
p3030701e.pdfExperiment guide, English374.94 KB