Experiment 4 (Part B)

Diffusion through a Colloid

Introduction

Diffusion refers to the process by which molecules mix up due to their kinetic energy. It is also the process by which molecules spread from due to the differences in concentration. The experiment was designed to test the diffusion in different settings. The part that was discussed is the diffusion in a colloid. Colloids are mixtures whose particles are larger than the size of a molecule but smaller than particles that can be seen with the naked eye. This colloid is composed of H20 and 5% gel. This part of the experiment is created to address the question: “Can molecular size affect rate of diffusion of particles in a colloid?”

Hypothesis

The tentative answer by which we all proposed is that the larger the molecular weight resulting in a large size of the molecules, the slower it would diffuse through the colloid.

EXERCISE 4: CELL TRANSPORT

PART BMATERIALS AND METHODS

The materials used are as

follows:

5% Hardened Gelatin

Potassium permanganate Solution

Methylene Blue

Congo Red

The Experimental

Procedure

Data AnalysisDistance Traveled (cm)

Time (min) KMnO4 Methylene Blue Congo Red

5 0.6 0.5 0.3

10 0.7 0.5 0.4

15 0.8 0.6

0.4

20 0.9 0.6 0.4

25 1.00 0.6 0.4

30 1.00 0.6 0.4

35 1.00 0.6 0.5

40 1.1 0.6 0.5

45 1.2 0.6 0.5

50 1.2 0.6 0.5

55 1.2 0.6 0.5

60 1.3 0.6 0.5

Results and Discussion

The colloid used as a medium made it possible to observe the effect of molecular mass in determining the rate of diffusion. Since a gel has a porous framework, substances with a high molecular mass will travel slower. This is due to the pores trapping the particles of the solution thus slowing their diffusion. Potassium permanganate, methylene blue, and congo red have the following molecular weights: 158.034 g/mol, 696.665g/mol, and 319.85 g/mol respectively.

It was hypothesized that molecules with smaller masses diffuse slower than those with higher molecular weights. In this table, it is clearly seen that KMnO4 traveled the farthest among the three solutions and Congo red has the least travelled distance. Looking at the molecular weights, KMnO4 has the lightest while the Congo red has the largest. With this information, it can be concluded that the larger the molecular weight resulting in a larger particle size of the substances’ molecules, the slower it will travel over a porous framework, e.g. a colloidal gel thus confirming the given hypothesis by the students.

However, it should be noted that the distribution of gel in the colloid is unequal. This results to the stopping of the solution at a certain distance.

Summary and Conclusion

This part of the experiment dealt with the effect of molecular weight on the rate of diffusion. By utilizing three reagents – potassium permanganate (KMnO4), methylene blue and congo red –with different molecular masses, to show the differences in the diffusion rate in a colloidal setting.

By observing and tabulating the data gathered from the experiment, it was found that potassium permanganate diffused the farthest along the colloid which was followed by methylene blue and congo red, respectively. By relating the masses and the size of the molecules with their diffusion along the gel, it can be seen that the lower the molecular mass, the less it travels, the slower the diffusion rate.