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Particle size: over nm, suspended; large particles or aggregates. May either scatter light or be opaque. Colloids are unlike solutions because their dispersed particles are much larger than those of a solution. The dispersed particles of a colloid cannot be separated by filtration, but they scatter light, a phenomenon called the Tyndall effect. When light is passed through a true solution, the dissolved particles are too small to deflect the light.
However, the dispersed particles of a colloid, being larger, do deflect light. The Tyndall effect is the scattering of visible light by colloidal particles.
All three are examples of colloids. Suspensions may scatter light, but if the number of suspended particles is sufficiently large, the suspension may simply be opaque and the light scattering will not occur.
Figure 2. Figure The table below lists examples of colloidal systems, most of which are very familiar. The dispersed phase describes the particles, while the dispersion medium is the material in which the particles are distributed. Dispersion Medium. That's where the camera is. So some of the light gets reflected towards us, or into the camera, and as a result that particle, we see that particle glowing red in color.
It glows red because it's reflecting red. And therefore that particle which it hit over here, that particular particle glows red. And then of course not all the light gets reflected.
Some of the light goes through as well, actually most of the light goes through. Let's draw that. So most of the light goes through. This is the light that didn't get scattered. Got that? This is the scattered light, and this is the light that didn't get scattered. So, most of the light goes through and then it hits another particle and then again scatters off from that. So another particle over here will glow, and the same process continues and as a result, all the particles which are in the path of that light end up glowing.
And since these particles are really really tiny, of course, I've drawn them to be pretty big over here, but they are really really tiny and there are so many of them that when we look at it, we don't get to see the individual particles, but all we see is a straight line. So we see a line that is glowing. And that line is what we perceive as the beam of light. That's that beam that we're seeing. So what we're actually seeing are the milk particles who are scattering light and as a result they are glowing.
And that's what shows the path of light. But why don't we see the path of light in a sugar solution? Don't they scatter light? Well, they too scatter light, in fact all particles can too scatter light, but here's the thing.
It turns out that if we do the analysis, it turns out that the amount of light that they scatter depends on the size of the particle. As the particle size become bigger and bigger, they tend to scatter more and more light. If the particle size becomes too small, then they do scatter light, but the scattered light will be so insignificant that we won't be able to see it. So a considerable amount of light will not reach our camera.
And that's what's happening over here. The particles in the sugar solution are so tiny that the scattered light is negligible, and that's why we can't see it. And in fact, analysis shows that if the particle size is roughly if the size of the particle is roughly smaller than one nanometer.
Right, this is not an exact value, it's a rough value. Unlike a solution, the dispersed particles can be separated from the dispersion medium by filtering.
Suspensions are considered heterogeneous because the different substances in the mixture will not remain uniformly distributed if they are not actively being mixed. A colloid is a heterogeneous mixture in which the dispersed particles are intermediate in size between those of a solution and a suspension. The particles are spread evenly throughout the dispersion medium, which can be a solid, liquid, or gas. Because the dispersed particles of a colloid are not as large as those of a suspension, they do not settle out upon standing.
The table below summarizes the properties and distinctions between solutions, colloids, and suspensions. Colloids are unlike solutions because their dispersed particles are much larger than those of a solution. The dispersed particles of a colloid cannot be separated by filtration, but they scatter light, a phenomenon called the Tyndall effect. Colloids are often confused with true homogenous solutions because the individual dispersed particles of a colloid cannot be seen.
When light is passed through a true solution, the dissolved particles are too small to deflect the light. However, the dispersed particles of a colloid, being larger, do deflect light see figure below. The Tyndall effect is the scattering of visible light by colloidal particles. You have undoubtedly "seen" a light beam as it passes through fog, smoke, or a scattering of dust particles suspended in air.
All three are examples of colloids.
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