The Effect of Molecular Weight on the Diffusion Rate of Substances

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The Effect of Molecular Weight on the Diffusion Rate in Substances

Nadjah B. Hadji Amer
Gladys A. Oliveros
Rochelle R. Yaῆez
Jan Remon B. Caliguid
Group 2- Sec. W78-1

August 14, 2013

A scientific paper submitted in partial fulfilment of requirements in Biology 101.1 under
Prof. Kimverly Hazel Coronel, 1st sem, 2013-2014


The effect of molecular weight on the rate of diffusion was assessed using the agar-water gel test. The agar-water gel set up was composed of a six petri dish of agar-water gel containing two wells. Pinch of potassium permanganate (KMnO4) and methylene blue (C16H18N3SCl) were simultaneously introduced to each dish and measured the distance and its rate. Methylene blue, having the largest molecular weight, displayed the smallest diameter 15.67 and diffused at the slowest rate (0.78mm/min). Next is potassium permanganate with a diameter of 13.33 mm and rate of diffusion of 2.54mm/min. The fastest is the potassium permanganate with 13.33 mm diameter and diffusion rate of 2.54 mm/min. Thus, the higher the molecular weight, the slower the rate of diffusion.


Diffusion is a process wherein molecules of gases collide and interact as a result of random motion. This eventually leads to the uniform distribution of the molecules of the involved gases throughout the system (Nave, 2008). Diffusion is a net movement of particles from an area of high concentration to low concentration (Traverso, 2004). Several factors may affect the rate of diffusion of substances. These factors include the particle size or the molecular weight of the substance, the temperature in the system, the concentration difference of the substances, the diffusion distance, the surface area, and the permeability of the barrier. The larger the particle, the greater the force needed to move the particle. Thus, at a certain temperature, a smaller particle diffuses faster than a larger one (Meyertholen,2012)
The hypothesis is to determine the

References: CITED Edition. McGraw-Hill, USA. p. 208.Meyertholen, E. (n.d.). Diffusion. Retrieved on July 30, 2012 from Nave, R. 2008. Diffusion and Osmosis. Retrieved on July 30, 2012 from  Silberberg, M. S. 2000. Chemistry 2nd Edition. McGraw-Hill, USA. p. 205. Traverso, M. 2004. Diffusion and Concentration Gradients. Retrieved on July 31, 2012from dynamic.htm

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