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Colloids - Suspensions - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Suspensions are mixtures of particles that settle out if let undisturbed. Suspensions can be filtered, while solutions cannot. Colloids are a type of mixture whose particles are held together through Brownian Motion, the erratic movement of colloid particles. Colloids cause the Tyndall Effect, or scattered light due to Brownian motion. The size of the particles found in colloids is smaller than those found in suspensions and greater than those found in solutions. One commonly known colloid is milk.

Alright, so types of mixtures that you're going to see one is homogenous mixture is also known as solution that the same through out and the next one is heterogeneous mixture and there're different types of heterogeneous mixtures where the particles are really big like solids or sands mixtures or things like that. But then there're ones that are very small such colloids and suspensions. Let's talk about those, suspensions are mixtures containing particles that settle out if left undisturbed meaning that like the particles are so large they have really big particles, they're bigger than 10 of the negative 6 which might seem quite small actually but compared to like atoms or compared to other particles typically in a solution which tenth to the negative ninth meters, they're actually quite large. Since that have large particles ad they have nothing to withhold them together they can be filtered, they actually can be separated out so types of suspensions that you'll see, that you'll come across that you might know if they're suspension or colloids or solutions even.

Blood if you leave blood, left undisturbed it will actually separate out, you can actually filter it out to separate it aerosols, corn start in water those kind of things are your types of suspensions. Another type of heterogeneous mixture is colloids, colloids are mixtures containing intermediate size particles held together through Brownian motion and Brownian motion we'll also get to in a second is what distinguishes suspensions versus colloids. So different types and examples of colloids would be milk where the particles are kind of big but not as big paint and fog where they actually stay together they don't filter out. So let's go and talk about what Brownian motion is, so Brownian motion is the erratic movement of colloid particles. So let's say take this picture for example we have out 2 larger colloidal particles like they could be proteins, they could be whatever and they're typically repulsed by each other, they have a repulsion but they might be attracted in other ways like other things within the solution, not the solution, the colloid will be attracted to it. So they have this like constant erratic movement of these particles. So how can we, if we're looking at 2 a suspension versus a colloid how can we like notice that one has Brownian motion one doesn't.

Well there's this thing called the "Tyndall effect" and the tyndall effect is that if you shine light through a colloid you're going to get a scattering of that light. So for example fog we know is a colloid, the reason you don't put your high beams on when you're driving through fog is because the Brownian motion of colloidal particles within the fog will shine that light right back in your eyes and actually like affect your driving negatively rather than positively. You'll actually see less of the road than if you put your regular low beam on or fog lights which are located lower which will then like light up the bottom of your driving. So that's the reason why, good example of real life example of fog and the tyndall effect.

But let's look at it here in the lab, let's talk about, so one of these guys is a colloid and one of these guys is a suspension. So if I shine my light through it, my light source which is this red laser beam, one of them should actually not be able to go through, the light should not be able to go through and the other one should. So let's actually test it out, so we have here if we put this through this side actually can't see the light source on the other side this is the colloid.

The colloid will stop the light it'll scatter the light and not allow it to go straight through. And this one you kind of probably already noticed that is a suspension is already starting to settle out but let's just test it out using the tyndall effect. Putting light through you can actually see, notice the light actually does go completely all the way through and it's got this like quite a little bit but it definitely like allows the light to go straight through whereas the colloid doesn't at all. So this tyndall effect through the Brownian motion and colloids and suspensions.