Lab 5 background

In this lab, we will study the movement of molecules.

The greater the movement of molecules, the greater the rate of diffusion.

Diffusion is the movement of molecules from an area of high to an area of low concentration.

Molecules move due to kinetic energy, the energy of motion.
Brownian movement is defined as random movement of small molecules.

As you increase the temperature, molecules move faster.
As you increase the size (the molecular weight), the movement of molecules is slower.

We will also study osmosis.  This is the movement of water from an area of high to an area of low concentration.
    hypertonic - means more solute and less water.  This means water will move out.
    hypotonic - means less solute and more water.  This means water will move in.
    isotonic - means there is the same amount of solute in and out of the cell so there will be no net movement.
 

There are 3 parts of the lab.

Part 5.1

Use agar.  It is like jello.  At room temperature, it is hard.

You will use 2 dyes of different weight and will measure the distance they travel through the agar.

Take 2 plates.
Record the diameter of the well at time 0
Put 5 drops of dye into one hole of the plate.
Put 5 drops of dye into the other hole of the plate.
Record the diameter of the wells at 10, 20 and 30 minutes.

You will then make a graph.  Will it be a line or a bar graph?

Part 5.2

Use a semipermeable membrane to do dialysis.  The membrane has microscopic holes so that only molecules smaller than the holes can move in.  Water can also pass through the membrane.

There are two parts of this experiment.
You will measure the weight of the dialysis tubing to determine the net movement of the water.
    If the weight of the tubing is heavier at the end of the experiment, then water moved in.
    If the weight of the tubing is less at the end of the experiment, then water moved out.

You will use Benedict's reagent to determine if glucose moved out of the bag.
    You will test the water outside the beaker and perform the Benedict's test.
    If it is positive, then glucose moved out.

Setup

Fill each bag with the 1M glucose solution.

Then put one bag into a beaker with water. Label this A. This solution contains less solutes than the bag and more water.  It is hypotonic. Water will move in.

Put one bag into a beaker with 1M glucose. Label this B. This solution contains the same amount of solutes as the bag.  It is isotonic.

Put one bag into a beaker with 3M glucose. Label this C. This solution contains more solutes than the bag.  It contains less water.  It is hypertonic.  Water will move out.

Weigh each bag before you start and then after 30 minutes.

In the second part of the experiment, take 2 test tubes. 
Place 1 ml of water in one test tube.
Take 1 ml of the solution from beaker A.
Perform Benedict's test.
Did glucose move out?

Part 5.3

I will demonstrate this part of the experiment.

I will take 4 testtubes.

One has 0.85% NaCl.  This is the isotonic solution
One has 0.05 % NaCl.
One has 0.5 % NaCl.
One has 10% NaCl.

I will add ox blood to each tube.

You will have to record the appearance of each and determine if water moved out or in relative to the cell.
    If water moves into the cell, the cell may just swell or it may burst.  The tube will be clear if the cell bursts.
    If water moves out of the cell, the cell will crenate, scallop or shrink.  The tube will be cloudy because there are      still cells present.

You also need to determine if the solution is hypertonic/hypotonic or isotonic.

You will compare everything to the 0.85% tube.  This is the tube that is isotonic.