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Colloids are fascinating mixtures in which fine particles are dispersed throughout a continuous medium. These particles, ranging from 1 nm to 1000 nm in size, are not visible to the naked eye alone.
The unique property of colloids lies in their ability to scatter light, a phenomenon famously known as the Tyndall effect. Colloids can appear cloudy or murky due to this effect, which distinguishes them from other mixtures such as solutions.
Examples of colloids include emulsions like milk, foams like whipped cream, and aerosols like fog. Each of these examples showcases how the dispersed particles interact with light. This scattering of light does not mean that the colloid is homogenous, but it certainly gives it unique properties.

Light scattering is an essential concept when discussing the Tyndall effect. It occurs when particles in a medium are large enough to disrupt the path of incoming light waves.
This disruption causes the light to deflect in different directions, creating a visible beam. This is why, in foggy weather or a smoky room, you might see beams of light from a flashlight or car headlights. The light interacts with the particles suspended in the air, scattering and making the light path visible.
Light scattering is a clear indicator of particle size in a mixture. In colloids, with their particle size ranging from 1 nm to 1000 nm, the scattering is significant enough to be observable. In contrast, in solutions, where particles are much smaller, such scattering cannot be observed.

Particle size is a crucial factor in determining whether a mixture will display the Tyndall effect. In colloids, the particle size allows the light to scatter, whereas in true solutions, the particles are too small for this to occur.
The distinction is clear when considering that colloidal particles range from 1 nm to 1000 nm. This size enables light interaction to the degree necessary for scattering.
In true solutions, on the other hand, particles are less than 1 nm, often at the molecular or ionic level. Such small sizes do not interfere with the path of light in a manner that scatters it, making the Tyndall effect absent in these mixtures.

Solutions in chemistry are homogenous mixtures where the solute particles are thoroughly dissolved in the solvent. The particle size in solutions is generally less than 1 nm, comprising either molecules or ions. This small size is why solutions do not show the Tyndall effect.
In solutions, the particles are so minuscule that light passes through without scattering. Examples of solutions include saltwater and sugar dissolved in water. In these cases, trying to observe a beam of light would be futile, as the light is not disrupted by the tiny particles.
Solutions exemplify one of the ways chemists can achieve a completely uniform mixture, free from the cloudiness often associated with colloids or suspensions.