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Solutions, colloids and suspensions – Tyndall effect, sols, adsorption and emulsions lab

ChemistryApplied & Practical ChemistryAges 11–12Virtual lab

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Use with my class

Compare screen: shine a laser (Tyndall effect), filter through filter paper, leave to stand and look through an ultramicroscope at six mixtures – salt, sugar, starch, milk, chalk and fine sand in water – then classify each as a true solution, a colloid or a suspension by particle size. Sols screen: prepare an iron(III) hydroxide sol by hydrolysing FeCl₃ in boiling water, an As₂S₃ sol, muddy water and a starch sol; then dialysis, electrophoresis and coagulation by electrolytes (Hardy–Schulze rule). Adsorption screen: Freundlich isotherms x/m = k·p^(1/n) at several temperatures. Emulsions screen: shake oil with water, with and without an emulsifier, and time the separation.

Lesson: Mixtures: true solutions, colloids, suspensions and emulsions; surface chemistry

What it shows

Mixtures in water differ in particle size. In a true solution the particles are below 1 nm: the liquid is clear, passes through filter paper and never settles. Colloid particles (1–1000 nm) also pass through filter paper and do not settle, but they scatter light, so a laser beam shows its path (Tyndall effect). Suspension particles are larger than 1000 nm: they block light, stay on filter paper and settle. Sols are colloids of solid particles; their electric charge explains electrophoresis and coagulation by ions of opposite charge. Particle sizes, flocculation values and Freundlich constants are typical or illustrative values.

How to use

On Compare, choose a Mixture, keep Laser beam on, press Filter, then Run to let it stand; press Record and choose the type to check your answer. On Sols, pick a Sol and an Experiment: Prepare, Dialysis, Electrophoresis or Coagulation, and press Run. On Adsorption, set the Temperature and Gas pressure, press Measure several times and turn on Log graph. On Emulsions, choose Oil and Emulsifier, press Shake and Run.

Parameters you can change

  • Screen Compare, Sols, Adsorption, Emulsions
  • Mixture Salt in water, Sugar in water, Starch in water, A few drops of milk in water, Chalk powder in water, Fine sand in water
  • Laser beam
  • Sol Fe(OH)₃ sol, As₂S₃ sol, muddy water (clay sol), starch sol
  • Sol experiment Prepare, Dialysis, Electrophoresis, Coagulation
  • Boiling water
  • Dialysis water temperature 20–80 °C
  • Electrophoresis voltage 0–250 V
  • Electrolyte NaCl, BaCl₂, AlCl₃, alum KAl(SO₄)₂·12H₂O, Na₂SO₄, Na₃PO₄
  • Electrolyte concentration in the tube 0.01–1000 mmol/L
  • Adsorption temperature 195–300 K
  • Gas pressure 0–100 kPa
  • Log graph
  • Oil vegetable oil, kerosene, castor oil
  • Emulsifier none, soap solution, detergent, egg yolk

Questions to explore

  1. Why does filter paper separate a suspension but not a colloid?
  2. Why does alum clear muddy water much faster than the same amount of sodium chloride?
  3. Why does an oil-in-water emulsion last much longer when soap is added?

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