Rate Of Diffusion Lab Report

The Effect of the Molecular Weight of a Substance to its Rate of Diffusion

Paulo E. Garcia
Group 2 Sec U-7L

October 16, 2014

ABSTRACT

The rate of diffusion was tested by using a petri dish with agar-water gel and three drops of different solutions. These solutions were observed for thirty minutes and measured every three minutes. The different solutions used are Potassium permanganate with a molecular weight of 158 g/mole diffused the greatest distance among the three, Potassium dichromate with a molecular weight of 294 g/mole diffused the lesser than that of Potassium permanganate, and Methylene Blue with a molecular weight of 374 g/mole diffused the least distance. Therefore, the lower the molecular weight of a substance,

One property that affected the diffusion of the three substances is the molecular weight. Potassium permanganate with a molecular weight of 158 g/mole diffused at a faster and bigger rate because it has less diffusible molecules allowing the substance to diffuse faster. Since Methylene Blue has the biggest molecular weight, it has more diffusible molecules making it hard for the substance to move resulting to short distance and slow diffusing rate.

Time (minute) Distance (mm) Potassium permanganate
(MW 158g/mole) Potassium dichromate
(MW 204g/mole) Methylene Blue
(MW 374g/mole)
0 5 5 5
3 7 6 5
6 8 7 5
9 10 9 6
12 11 10 6.5
15 12 11 7
18 13 12 8
21 16 14 10
24 18 16 11
27 20 16 11
30 20 18 12

Figure 3 shows the relationship of the partial rate of diffusion of the three substances. Figure 4 presents that among the three substances, potassium permanganate had the highest rate of diffusion of 0.57 mm/min, followed by potassium dichromate with a rate of diffusion of 0.43 mm/min, and with the least rate of diffusion of 0.23 mm/min, methylene

The molecular weight of a substance has a great influence to its rate of diffusion. The results from the experiment showed that a substance with a lower molecular weight like potassium permanganate has a high rate of diffusion unlike other substances with high molecular weight because of the number of diffusible molecules. If there is a high quantity of diffusible molecules present in a substance, most likely, it will have a slow rate of diffusion.

More accurate results can be achieved by considering various factors like the correct handling of specimens, the type of medium where diffusion is taking place, temperature, equal amount of substance used, and others.

LITERATURE CITED

Brown, LeMay, Bursten. 2005. Chemistry: The Central Science. 10th ed. New Jersey: Pearson Prentice Hall.p.426.
M.Hein, S. Arena. 2011. Foundations of College Chemistry. 13th ed. New Jersey: John Wiley & Sons,