Osmosis and Diffusion Lab

Topics: Osmosis, Diffusion, Molecular diffusion Pages: 9 (2240 words) Published: November 1, 1996
The purpose of this lab was to observe the rate of osmosis and diffusion, as well as the effect of molecular size of the particles on this rate. Part I of the lab was a demonstration of osmosis and diffusion, that dealt with raisins in different liquid environments, each with a different concentration of sugar. Part IV of the lab was using the same idea as the demonstration, by putting objects in different concentrations of a substance; in this case elodea leaves in salt water. In both cases, the objects in a greater concentration of the substance were stripped of their water. However, where there was a little or no concentration of sugar or salt, the objects did not lose their water, and in the case of the raisin, became saturated with excess water. Part II of the lab dealt with the rate of osmosis, and how molecular size was a factor on it. The purpose was to see how easily molecules of smaller diameter, which were starch molecules, would pass through an artificial membrane, as opposed to how difficult it would be to pass through in the case of larger molecules, which were IKI molecules. Results were that the smaller substance passed though the membrane easily and rather quickly, and the larger substance did not penetrate the membrane whatsoever. Part III of the lab was to view the effect of molecular size on the rate of diffusion. Two substances, both being of different molecular size were placed in the same environment. Results were that the substance with the smaller molecules, diffused farther away from where it was placed than did the substance of greater molecular size in the same amount of time.

The title of this lab is 'Osmosis and Diffusion.' Both these terms deal with the transfer of a substance from one place to another, depending on where there is more space. Diffusion is the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration. Diffusion can be the transfer of anything anywhere. However, that is not true for osmosis. Osmosis is diffusion, but a specific type of diffusion. Osmosis is only the diffusion of water molecules through a selectively permeable membrane. The comparison of the concentration of a substance on one side of the membrane as opposed to the other is called the concentration gradient. If an object has a lower concentration of a substance than does it's surroundings, then the object is called hypotonic. If it has the same concentration of a substance as it's environment, then it is isotonic. If the object has a higher concentration of a substance than does it's environment, then it is hypertonic. Does the difference in the concentration gradient effect the rate of diffusion or osmosis? Are osmosis or diffusion also affected by certain aspects; such as molecular size or weight? The answers to these questions were tested and answered during the different phases of this four part lab.

Part I of the lab was the demonstration. Three raisins of roughly the same size were taken from a box of raisins, and each were placed in a different environment. The control was the one of the raisins in an empty container. One of the raisins was placed in a container filled with distilled water (0% sugar concentration), and the other raisin was placed in a container filled with karo syrup, which is a super saturated sugar solution. The independent variables here are the water and the karo syrup, while the independent variable is the rate of change in the size of the raisin due to the direction the water will move; either into or out of the raisin itself. If there is a movement in water at all, then osmosis will have taken place, since osmosis is the transfer of water across a membrane; in which this case it is the raisin's outer skin. The hypothesis was that if there is a greater concentration of sugar outside of the raisin, osmotic pressure will cause the raisin to become dehydrated, and if there is less sugar outside the raisin,...
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