Hi. It’s Mr. Andersen and today
I’m going to show you the diffusion demo of the lab one diffusion and osmosis lab. And
so first of all to review what is diffusion? Diffusion remember is the movement of molecules
from an area of high concentration to low concentration. It’s just do to molecular motion.
So if we put some food coloring in water, the food coloring is just going to move apart.
And that’s because the molecules are moving. And so it’s going to move apart until the
concentration throughout is going to be the same. And so basically what you’re going to
try answer after watching this diffusion demo is rank the following from smallest to largest.
Starch, glucose, water, the pores in the dialysis tubing and then finally IKI or Lugol’s solution.
So first of all I should probably describe what all of these things are. Starch is going
to be a polysaccharide. And so before we talk about what a polysaccharide is, we should
talk about what a saccharide is or a monosaccharide. Glucose is a monosaccharide. That means that
it’s essentially C 6 H 12 O 6. And so it is six carbons organized kind of in a hexagon.
It’s got a lot of oxygen and hydrogen around the outside. And so that’s a monosaccharide.
If we look at starch, so starch like that’s found in a potato, starch is going to be a
number of monosaccharides attached together. And so we call that a polysaccharide. And
it’s not just going to be a few like I’m drawing right here. A good starch or a good polysaccharide
is going to have thousands of these glucose molecules attached together. Over and over
and over. And so starch and glucose are both sugars. Both carbohydrates. Now it’s just
that starch happens to be a little bit bigger. Hopefully you’re familiar with water. Water
is going to be made up of two things. You’re going to have one oxygen atom. And then you’re
going to have two hydrogen atoms attached on the side. And so water is simply H2O. Next
one is the pores in the dialysis tubing. So we’re going to put some liquid inside a dialysis
tubing. We’ll seal it off on either side. So it’s going to be sealed off like that.
But the pores in the dialysis tubing are going to be these microscopic holes that are in
the dialysis tubing. Remember dialysis tubing is used kidney dialysis. And so you can’t
really even see the holes at all. But they’re really really tiny. And then the last thing
is Lugol’s solution or IKI. The big thing that you’re looking for here is going to be
the iodine that’s found in the Lugol’s solution. The big thing that you need to know is that
if you ever have Lugol’s solution and starch in the same place at the same time, you’re
going to get a real blue color. So it turns to a blue color. In other words if you were
to take a potato and then just put Lugol’s solution on it, you’re going to get blue coloration
on that potato. That’s just due to a chemical reaction. But we use Lugol’s solution or IKI
as an indicator of starch. So where we’re going to find starch. And so after you watch
this demo what you want to be able to do is rank the following, starch, glucose, water,
pores in the dialysis tubing and then finally IKI. You want to be able to rank all of those
from the smallest to the biggest. Okay. The video, since I’m at home you can tell, I don’t
have the chemistry equipment right here. And so I’m going to grab a video from YouTube.
This one I am taking from RdtoUtopia and it’s got quite a few hits. 32,000. It’s been around
for awhile. But it just shows you a demonstration of this. And so thank you to RdtoUtopia. You
probably want to visit it to see the whole video. I’m just going to show you a portion
of it. And if you go there you’ll also see a really good video of a dancing robot toy,
which is worth the trip as well. And so thank you for that. But this is the diffusion experiment.
So first of all let me kind of get it started. So let’s get it started. Okay. So let me stop
it right there and draw on it a little bit. So what do we have in this experiment? We
have in here a bag, this is that bag of dialysis tubing. And you can see that it’s kind of
a whitish kind of a yellowish color. It’s kind of sealed off on the sides. And so if
we look at what’s in there, inside here we’re going to have two things. We’re going to put
starch in it to begin with, starch solution. And then we’re also going to put glucose inside
there. And then the other thing we put just to dissolve those is going to be water. So
we have those three things inside the dialysis tubing. Outside the dialysis tubing, so in
this area out here in the liquid portion of the beaker we’ve got the, let me draw an arrow
here. So out here we’ve got water. And then we’ve also got the Lugol’s solution. So we
have this IKI. Alright. The other thing you normally do before you start this is you start
looking at the presence of glucose or the absence of glucose. And so you do that using
this. These glucose test strips. Right over here. They’re used to monitor glucose levels.
So if you’re a diabetic it’s a good way to see how much glucose there is in your urine
is what we’re looking at. Because if you have high glucose levels it’s an indicator of problems
with regulating blood sugar. And so what you do is you put a strip into the fluid. And
then it will change to a color. So it will start as a blue color. But it can move all
the way up to a red color. This is what I use in class to figure out if there’s glucose
present. And so if we were to take this glucose strip and put it inside this, are we going
to find glucose? The answer is yes. So we’ll have a positive out here. And I just said
over here a second ago that there’s glucose in there. So that shouldn’t be a surprise.
If we were to take a test strip and look out here we’re going to find glucose out here.
We’ll have a negative for that. So there’s no glucose out here to start with. But there’s
going to be glucose inside. And so this is what it looks like when it starts. And I’m
going to have to get rid of this writing for a second. And then we’ll play the video for
a bit. And you can see immediately that it starts to get a coloration change inside the
beaker. And let me kind of move it out. Move it up a little bit faster. So we’ll look all
the way out here. And I’m going to play it there. So this is like ten minutes later.
And so now, ten minutes later, when you pull it out we’ve got the same dialysis bag. It
seems like the color has changed a little bit. If we were to now test it for glucose
what we would find is that there is still going to be a positive for glucose inside.
But now if we look out here there’s going to be a positive for glucose out there with
a test strip. And so that’s kind of all the diffusion demonstration is. So now your goal
is to figure out from smallest to largest, can you rank these five things? And you’re
going to have to use an understanding of diffusion. But you’re also going to have to use logic
to figure that out. And I’m not going to tell you the answer. So I hope that’s somewhat