In the discussion of the colloid system chapter material there is a sub-discussion that explains the Tyndall effect. Launching the official website of the Ministry of Education and Culture, the Tyndall effect means the scattering of light rays by colloidal particles. This is due to the size of the colloid molecule which is quite large.
The Tyndall effect was discovered by John Tyndall (1820-1893), an English physicist. In 1869, Tyndall discovered that if a light beam is passed through a colloidal system, the light beam will appear. However, if the same beam of light were passed through a true solution, the beam would not be visible.
History of John Tyndall
The figure of John Tyndall is a physicist from Ireland who was born on August 2, 1820. Born to a family that is less well off but very caring and views the importance of science and education. After graduating from school, John Tyndall worked as a surveyor and some time later changed professions to become a professor.
Around 1859, Tyndall began researching the heat radiation of water vapor that forms clouds, ozone, hydrocarbons, and CO2 gas. With his assembled spectrophotometer, he measured the absorption of gases in the air. From the results of his research, Tyndall found the fact that ozone, hydrocarbons, and carbon dioxide absorb more heat than other gases.
But the greatest of all is the water vapor that surrounds the earth. Through this research, Tyndall discovered the phenomenon of light scattering by colloidal particles, which was later known as the Tyndall effect. In the event of the greenhouse effect and the phenomenon of colored skies, the causes of the Tyndall effect can also be studied.
The greenhouse effect causes the earth to get warmer and hotter. According to Tyndall’s spectrophotometer measurements, gases in the atmosphere have different abilities to absorb heat. Gases that have a high heat absorption capacity are called greenhouse gases.
The discovery of the Tyndall effect can also explain why the sky during the day is blue, while when the sun sets on the western horizon it is orange or red. This is due to the scattering of sunlight by colloidal particles in space, and not all frequencies of sunlight are scattered with the same intensity. This is what explains what happens to the colors of the rainbow.
John Tyndall died on December 4, 1893 at the age of 73 due to an accidental drug overdose.
Tyndall Effect on the Colloidal System
Have you ever noticed the atmosphere when watching a movie in the cinema? When the projector lamp is turned on, it will be clear when there is smoke or dust passing through it, so that the film image on the screen becomes blurry or unclear. This is due to the scattering of light coming from particles of smoke or dust, which reduces the penetrating power of the projector lamp. This scattering of light is known as the Tyndall effect on colloids.
Quoted from kelaspintar.id, Tyndall effect itself is a phenomenon of scattering of light when the material is hit or irradiated by a beam of light. When a beam of light is passed through a solution, the light is transmitted. Meanwhile, if a beam of light is passed through a colloidal system, the colloidal particles will scatter the light.
These colloidal properties can be used to distinguish true solutions and colloidal systems. True solutions do not scatter light. This means, true solutions do not have Tyndall effect while colloidal systems are able to scatter light which means colloidal systems have Tyndall effect properties.
A Brief Explanation of Colloidal Systems and Their Properties
Here are some properties of colloidal systems that are not just the Tyndall effect:
1. Tyndall Effect
As previously explained, this effect is a symptom of the scattering of light rays (light) by colloidal particles. This is due to the size of the colloid molecule which is quite large.
Tyndall effect also means the effect that occurs when a solution is exposed to light. When the solution is irradiated with light, the solution will not scatter light. Whereas in a colloidal system, light will be scattered. This happens because colloidal particles have relatively large particles to be able to scatter the light. On the other hand, in solution, the particles are relatively small, so that the scattering occurs is very small and very difficult to observe.
2. Brown’s Motion
Brownian motion can also be referred to as the motion of colloidal particles that move straight but erratically (random/irregular motion). When a colloid is observed under an ultra microscope, we will see the particles move in a zig-zag shape. This zigzag motion is called Brownian motion.
The particles will always be in motion. The motion can be random as in liquids and gases (called Brownian motion), whereas in solids it only oscillates in place (excluding Brownian motion).
For colloids with a liquid or gas dispersion medium, the movement of the particles will result in collisions with the colloidal particles themselves. The collision took place from all directions. Because the particle size is quite small, the collisions that occur tend to be unbalanced. So there is a resultant collision that causes a change in the direction of particle motion so that there is a zigzag motion or Brownian motion.
The smaller the colloid particle size, the faster Brownian motion occurs. Similarly, the larger the colloidal particle size, the slower the Brownian motion that occurs. This explains why Brownian motion is difficult to observe in solution and is not found in heterogeneous mixtures of liquids and solids (suspensions).
Brownian motion is also influenced by temperature. The higher the temperature of the colloidal system, the greater the kinetic energy of the particles of the dispersing medium. As a result, the Brownian motion of the particles of the dispersed phase accelerates. Vice versa, the lower the temperature of the colloidal system, it can be ascertained that the Brownian motion slows down.
3. Adsorption
Adsorption is the absorption of particles or ions or other compounds on the surface of colloidal particles caused by the large surface area of the particles. Adsorption must be distinguished from absorption which means absorption that occurs inside a particle.
Example:
(i) Fe(OH)3 colloid is positively charged because its surface absorbs H+ ions.
(ii) Colloidal As2S3 is negatively charged because its surface absorbs S2 ions.
4. Colloidal Coagulation
Coagulation can be interpreted as agglomeration of colloidal particles and form a precipitate. With the occurrence of coagulation, it can be interpreted that the dispersed substance no longer forms colloids.
Coagulation can occur physically such as heating, cooling and stirring or chemically such as addition of electrolytes, mixing colloids with different charges.
5. Protective Colloid
Protective colloids are colloids that have properties that can protect other colloids from the coagulation process.
6. Dialysis
Dialysis is the separation of colloids from interfering ions by flowing liquid mixed with colloids through a semipermeable membrane that functions as a filter. This semipermeable membrane can be passed by liquid but not colloidal, so colloid and liquid will separate.
7. Electrophoresis
Electropheresis is the separation of charged colloidal particles using an electric current.
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