Properties of colloids
To show some properties of colloidal solutions.
Cosa imparano gli studenti
La scienza alla base di questo esperimento
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.
Attrezzatura utilizzata
- Provette — 1473,60
- Portaprovette — 5423.30
- Spatula double end — 5460.34
- Bruciatore ad alcool — 5514.10
- Tripod stand — 5533.10
- Wire gauze — 5534.25
- Beaker 50 ml — 1118.15
- Glass rod — 1444.10
Sostanze chimiche e reagenti
- Sulphur — R:11-16 S:41
- Cloruro di sodio
- Ethanol — R:11 S:7-16
- Acqua distillata
- Milk
Note sulla sicurezza
- Prestare attenzione durante l'uso del bruciatore e degli oggetti in vetro caldi.
Domande per gli studenti
- 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?
Cosa aspettarsi
<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>
Smaltimento
Smaltire le soluzioni nel contenitore per i rifiuti liquidi.
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