Sept. 26: Homework and Lab Report Handout

Please catch up on your reading and turn in all of your homework this week!!!

If you have completed them during our lab time, please write either the cell lab report (there is no electronic version of this lab)or
The diffusion Lab report (below) answering all the questions associated with each lab.
Rate of Diffusion

Information

Scientists know that all matter is made of molecules and that these molecules are always moving—that is, the molecules present in matter have a kinetic energy. In liquids and gases the molecules can move from one place to another. Of course, as they move, they are constantly bumping into one another so that the movement is not in a direct line.

Diffusion can be defined as the random movement of molecules (because of kinetic energy) from a place of higher concentration to a place of lower concentration. Diffusion can happen through a membrane, too, if the material is permeable. Cell membranes are permeable to certain materials. In fact, that is how some material gets into a cell and how wastes get out.

A chemical called potassium permanganate (KMnO4) dissolves easily in water, and when it is dissolved, it will diffuse through a cell membrane. In addition, KMnO4 is purple, so it is easy to see. In this lab you will put pieces of potato into KMnO4 solutions and see how concentration and time affect the amount of diffusion into the potato.

Procedure

Part A
KMnO4 (Potassium Permanganate is Caustic!! Wear goggles and gloves and Handle Carefully!!!!)

1. Use a scalpel to cut a 1 cm thick slice from a potato. Then cut the slice into cubes that are 1 cm on a side.
2. Label 3 beakers: 4%, 2%, 1%, and 0.5% KMnO4. Add the same volume of each solution to each beaker (just enough to cover the potato piece).
3. Carefully place a potato cube into each beaker. Leave cubes in the solution for 30 minutes.
4. After 30 minutes, remove each cube from its beaker with forceps and cut the cube in half. Use a ruler to measure how far the solutions diffused into the cube. Dry the scalpel before you use it for each cube. Record the date in the table below:

Table 1: 30 minute incubation
Cube Number KMnO4 Concentration Diffusion (mm)
1 4%
2 2%
3 1%
4 0.5%
1. What is the relationship between concentration of the solution and amount of diffusion?



2. What is the ratio of the amount of diffusion to concentration (4%: 2%: etc.)




3. Graph your data.

Part B:

1. Place 6 of the potato cubes into a beaker.
2. Pour just enough KMnO4 solution into the beaker to cover the cubes.
3. Write down the start time here:
4. After 5 minutes, use forceps to remove one of the cubes from the solution. With a clean scalpel, cut the cube in half and measure the distance, in millimeters, that the solution has diffused into the cube. In Table 2, record the length of time the cube was in the solution and the distance that the solution diffused into the cube.
5. Repeat step 4 at 5 minute intervals until all the potato cubes have been cut and measured. Record the data for each cube.

Table 2: Diffusion of 4% KMnO4 into 1 cm Potato Cubes Over Time
Cube Number Time (min.) Diffusion (mm)
1 5
2 10
3 15
4 20
5 25
6 30


1. Which cube showed the greatest amount of diffusion:
2. Which cube showed the least amount of diffusion:
3. What is the relationship between the time and the amount of diffusion?


4. Can this relationship be expressed mathematically? If so, how?



5. Graph your data
6. Is it possible to make predictions from this model? What is your prediction?




7. Explain what is happening on a molecular level.






8. Why is it important the blade of the scalpel be dried between uses?




9. What effect would an increase in temperature have on the rate of diffusion?








10. Design an experiment that would test your