THE EFFECTS OF MOLECULAR WEIGHT ON THE RATE OF DIFFUSION OF SUBSTANCES

THE EFFECTS OF MOLECULAR WEIGHT ON THE RATE OF DIFFUSION OF SUBSTANCES

PRINCESS AYNAH D. SANGGACALA

Biology 101.1
Professor Christina A. Barazona
September 15, 2014

THE EFFECTS OF MOLECULAR WEIGHT ON THE RATE OF DIFFUSION OF SUBSTANCES

In partial fulfillment of the requirement
For Biology 101.1

By
Princess Aynah D. Sanggacala

Professor Christina A. Barazona
September 15, 2014
ABSTRACT

The effect of molecular weight on the rate of diffusion was figured by using a glass tube and an agar-water gel. In glass tube test, two cotton plugs submerse with two different substances – hydrochloric acid (HCL) and ammonium hydroxide (NH4OH) on the other end of the tube. By their molecular weight, NH4OH has a small molecular weight that diffuses at a faster rate. While the formation of a white cloud was first occurred at the end of the tube containing HCL with a large molecular weight. In agar-water gel test, using agar plate and agar-water gel, 2 different substrate were tested- potassium permanganate (KMnO4) and methylene blue (C16H18N3SCl). By dropping it on a agar plate, methylene blue has a slowest diffusion rate and large molecular weight than potassium permanganate. Thus, the greater the molecular weight, lesser the rate of diffusion.

INTRODUCTION Diffusion is a passive transport. It is results from the thermal and random movement of molecules. Diffusion is a process of equalization which involves movement of molecules from an area of high concentration to an area of low concentration. There are several factors/influence may affect the rate of diffusion of substances. These factors include concentration of gradient, size of molecule involved, distance the molecules has to travel, temperature, solubility of the molecule and surface area of the membrane over which the molecule can work. The larger the particle, the greater the force needed to move the particle. Like the relationship between the molecular weight and the rate of diffusion. In temperature, the smaller the particles it will diffuse faster than larger particles. Thus, the hypothesis of the study is that the rate of diffusion is inversely proportional to the size of particles. The effect of molecular weight on the rate of diffusion can be observed by glass tube test. Placing cotton on the end of each glass tube with a 2 different solutions soaked on it; there is an observation that there is a formation of white ring around the tube containing HCL. The two substances both react to form NH4Cl, and the white smoke may be the evidence that molecules have diffuse from the wet cotton. The agar-water gel test is involving by dropping a different solution in a separate agar plates, measuring their diameter at regular intervals. In the experiment, the solutions used were potassium permanganate and methylene blue. The three substances have different colors and easily identify the measurement of the diameters. This study aimed to figured out the effects of the molecular weight on the rate of diffusion of substances with respect to time via the agar-water gel test. The purpose of this experiment was to identify the factors that affect the diffusion of rate of substances and explain the effect of the molecular weight on the diffusion rate of substances.

MATERIALS AND METHODS

Materials for Glass Tube Testing
Glass tube
Cotton
Rubber Bands
Substances
Hydrochloric acid
Ammonium hydroxide
Glass Tube Set-up
1. A glass tube was placed on an iron stand, held in place by rubber bands.
2. Two cotton plugs soaked in Ammonium Hydroxide and Hydrochloric Acid on the end of each glass tube.
3. The set-up repeats three times and it was observed that there is a white smoke appeared on the glass tube.

Materials/Equipment for Water Agar-gel Testing
6 Agar Plates
Ruler
Cellphone Timer
Substances (powder)
Potassium Permanganate
Methylene Blue
Water Agar-gel Set-up An agar plates containing 2 solutions different molecular weight used; potassium permanganate (KMnO4), a red solution with a molecular weight of 158g/mole and methylene blue (C16H18N3SCl), a blue solution with a molecular weight of 320g/mole. A drop of each solution was introduced in each agar plates that used; 3 agar plates for KMnO4 and 3 agar plates for C16H18N3SCl. The diameter (mm) of each solution was recorded at 0mins.

The measurement of the diameter of each solution was recorded at a regular 15minutes for 1hour. Using a ruler every interval, measure the diameter. After gathering the data, compute the rate of diffusion for the two substances using the formula: Rate=

The average rate of diffusion of each substance against molecular weight was plotted. Partial rates of each substance at a specific time were plotted for analysis and interpretation.
RESULTS
Based on the molecular weight of HCL 36.46 g/mole and NH4OH 35.05 g/mole, the HCl diffuse on a slower rate. Since NH4OH diffused at faster rate, it reached the HCl side faster than HCl reaching the NH4OH side of the glass tube. This resulted in the formation of the white clouds as the first indication that the NH4OH molecules have met and reacted with HCl molecules from the other end of the glass tube nearer the HCl. In the next experiment is about the potassium permanganate and methylene blue. The hypothesis if the molecular weight affects the rate of diffusion of substances, then the higher the molecular weight, the slower was the diffusion.

FIG . Potassium permanganate and Methylene blue drops at 0min
When the potassium permanganate and methylene blue drops at 1 hour, the observation showed that molecular weight increase the rate of diffusion is decreasing. This will be shown in a table and figures. TABLE 1 shows it. Between the relationship of time and diffusion rate, as the time increasing the partial diffusion of each substances generally decreases. This will be shown in a tables and figures. TABLE 1 shows it.
DISCUSSION
Plugging cotton on the end of each glass tube NH4OH gaseous vapor particles diffuse or travel through the air a lot quicker than HCl because they are lighter in weight. Thus the cloud will be created closer to the NH4OH cotton ball. Also the white cloud formed in HCl because it has a greater molecular weight than NH4OH. The hypothesis is “the rate of diffusion is dependent on the size or molecular weight of the diffusible molecules. The methylene blue has larger molecular weight than potassium permanganate so by the hypothesis it is valid. On the relationship between the time and the rate of diffusion, the time depends on the rate of diffusion as shown on the Table1, it is clearly stated there. Observing the Figure 2 as the time increases, the distance of the millimeter increase.
TABLES AND FIGURES
Table 1. Diffusion rate of methylene blue and potassium permanganate
Methylene Blue
(MW:320g/mole)
Potassium Permanganate
(MW:158g/mole)
Time
(min)
Distance(mm)
Rate (mm/min)
Time
(min)
Distance(mm)
Rate (mm/min)
0
18.33
0
0
16.67
0
15
22.33
0.27
15
22.33
0.45
30
23.33
0.17
30
37.67
0.37
45
24.67
0.14
45
30.33
0.30
60
25.33
0.12
60
34
0.29

Figure 1. Relationship between the Molecular Weight and Rate

Figure 2. Relationsip between time and distance
CONCLUSION
The effect of the molecular weight and the rate of diffusion were figured out using the agar-water gel set-up. In 6 agar plates that used, the 3 of it was dropped by a potassium permanganate while the other 3 was dropped by methylene blue. The diameters of the colored areas were measured and record it in regular 15 minutes interval. For overall results Methylene blue produced the smallest diameter with 22.98mm as compared to potassium permanganate with 26.4mm. In our experiment it supports the hypothesis that the greater the molecular weight the lesser the rate of diffusion. As we all know that the molecular weight of methylene blue is 320g/mole while potassium permanganate is 158g/mole.

REFERENCES
Internet
http://biology.kenyon.edu/HHMI/Biol113/diffusion.htm https://www.academia.edu/1776814/The_Effect_of_Molecular_Weight_on_the_Rate_of_Diffusion_of_Substances Everett, G.W and G.W Everett. Jr. (nd.). Diffusion of gases and Graham’s Law. Retrieved September 14, 2014 from http://www.cerlabs.com/experiments/1087540412X.pdf http://www.answers.com/Q/Relation_between_rate_of_diffusion_and_molecular_weight http://www.flinnsci.com/documents/demopdfs/biology/bf10110.pdf
Manual
Biology 101.1 Laboratory Manual: Introduction to Biological Sciences.MSU-IIT Iligan City

References: Internet http://biology.kenyon.edu/HHMI/Biol113/diffusion.htm https://www.academia.edu/1776814/The_Effect_of_Molecular_Weight_on_the_Rate_of_Diffusion_of_Substances Everett, G.W and G.W Everett. Jr. (nd.). Diffusion of gases and Graham’s Law. Retrieved September 14, 2014 from http://www.cerlabs.com/experiments/1087540412X.pdf http://www.answers.com/Q/Relation_between_rate_of_diffusion_and_molecular_weight http://www.flinnsci.com/documents/demopdfs/biology/bf10110.pdf Manual Biology 101.1 Laboratory Manual: Introduction to Biological Sciences.MSU-IIT Iligan City