The Effect of Molecular Weight on the Rate of Diffusion of Potassium Permanganate (Kmno4), Potassium Dichromate (K2Cr2O7) and Methylene Blue ¹

1556 Words Apr 10th, 2013 7 Pages
The Effect of Molecular Weight on the Rate of Diffusion of Potassium permanganate (KMNO4), Potassium dichromate (K2Cr2O7) and Methylene blue ¹


The effect of molecular weight on the rate of diffusion was determined using the Agar-water Gel Test. One drop of potassium permanganate (KMNO4), potassium dichromate (K2Cr2O7) and methylene blue were used. Each substance has a respective molecular weight of 158 g/mol, 294g/mol and 374 g/mol. The diameters (in millimeter) were measured over time and the partial rates were computed. Results showed that as the time elapsed increases, the rate of diffusion decreases and the substance with the lowest molecular weight had the highest diffusion. Thus, the rate of diffusion of
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Then results were analyzed.


Results showed that the diameters of potassium permanganate, potassium dichromate and methylene blue increases over a progress of time but it had similar measurements (5 mm) at time zero. This was supported by the illustration of the set-up at the beginning of the experiment in Figure 1, which shows that the drops of each substance were of the same sizes. The measurements of the diameter did not show much change towards the end of the experiment. After thirty minutes, potassium permanganate had the largest (19 mm) and methylene blue had the smallest diameter (11 mm). As illustrated in Figure 2, the size of the drops of potassium permanganate and potassium dichromate were comparatively bigger in contrast with methylene blue.

Computing for the partial rates and average rates of diffusion, potassium permanganate still had the highest average rate of diffusion (0.40 mm/min) followed by potassium dichromate (0.30 mm/min) and methylene blue (0.20 mm/min). It was also observed that the partial rates slowed down over time and remained constant for some instances. These observations were clearly represented in a graph at Figure 3, where the partial rates of diffusion, on the average, decreases as the time elapsed increases but the inaccuracies in measuring the diameter