الكيمياء

Properties of colloids

To show some properties of colloidal solutions.

المادة، والمخاليط، والمحاليل
colloids; Tyndall effect; coagulation

ما يتعلمه الطلاب

الجانب العلمي وراء هذه التجربة

Colloidal solutions pass unchanged through filter paper, quite the opposite of suspensions. Colloids also diffract light in a particular way called the Tyndall effect, and can be coagulated by electrolytes to give precipitates which can then be filtered.

Colloids collect electric charges on the surface of their particles and the repulsion of these charges, besides solvation, is the cause of the stability of the solutions.

The Tyndall effect and flocculation or coagulation due to the addition of electrolytes are other important properties.

المعدات المستخدمة

  • Test tubes — 1473.60
  • Test tube holder — 5423.30
  • Spatula double end — 5460.34
  • Spirit burner — 5514.10
  • Tripod stand — 5533.10
  • Wire gauze — 5534.25
  • Beaker 50 ml — 1118.15
  • Glass rod — 1444.10

المواد الكيميائية والمواد الكاشفة

  • Sulphur — R:11-16 S:41
  • Sodium chloride
  • Ethanol — R:11 S:7-16
  • Distilled water
  • Milk

ملاحظات السلامة

  • Take care when using the burner and hot glassware.

أسئلة للطلاب

  • Record your observations. What can you say about the two solutions? What is the name of this phenomenon?
  • What happens to the colloids on adding sodium chloride and after boiling?
  • What can you say about the diluted milk solution?

ما يمكن توقعه

<p>The light beam passes through the solution of sodium chloride without leaving any trace. The light ray diffracts light in its path through the colloidal solution, creating a cone effect.</p><p>This phenomenon is called the Tyndall effect, i.e. diffraction of light due to the presence of particles which interact with light.</p><p>Adding sodium chloride and boiling the solution causes coagulation of particles and consequent loss of colloidal properties due to the formation of larger clusters.</p><p>The diluted milk also shows the Tyndall effect because it contains droplets of fat/oil dispersed as a colloidal solution.</p><p>In this case micelles are constituted of fat and protein particles which present a hydrophobic part and a hydrophilic part.</p>

التخلص

Dispose of the solutions into the liquid wastes container.

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