Table of Contents
Do Larger Things Diffuse Faster?
Overview
In this activity, you will compare the rate of diffusion of two different dyes through agar. Agar is a gelatinous substance derived from a structural carbohydrate found in seaweed. It is often used in cooking as a vegetarian alternative to gelatin and can be used as a thickener. Microbiologists pour plates of agar containing nutrients in order to isolate and grow bacteria and other microbes. As with gelatin, the long fibrous nature of this structural carbohydrate permits it to be melted and tangled together in a mesh-like network where the spaces between molecules are filled with solution. Altering the amount of fluid solution will change the pores between fibers. More fluid will create a looser gel that has larger spaces between molecules. Reducing the fluid solution volume will conversely create a stiffer gel with smaller spaces between fibers.
Materials
Each lab group will need the following materials:
- 2 test tubes containing agar
- malachite green (365 g/mol)
- potassium permanganate (164 g/mol)
- test tube rack
- wax pencil
- ruler
Before You Begin
Hypothesize which solution will move faster through the agar and provide a reason.
Method
- Mark the top of the agar on the outside of the tube (the starting point) using the wax pencil.
- Add 10 drops of malachite green to one tube and 10 drops of potassium permanganate to the other.
- Take note of the time.
- At 20 minute intervals, measure the distance from the top that the dye has moved down through the agar in millimeters. Record your data in your notebook. Do this for at least 1 hour.
- Plot the data using Excel, Plot.ly, or Google sheets and compare the trends. Describe the rate of diffusion for each.
Conclusion
- Which solution actually moved faster?
- Did this meet your expectations?
- Propose a reason why a certain dye moved faster.
