The Effects Of Concentration On Osmosis

Introduction:

This experiment was used to examine the hypothesis that: Osmosis is dependent on the concentrations of the substances involved.

Diffusion is the passage of solute molecules from an area of high concentration to an area of low concentration (Campbell & Reece, 2005). An example is ammonia diffusing throughout a room. A solute is one of two components in a chemical solution. The solute is the substance dissolved in the solution. The solvent, the other component, is any liquid in which the solute can be dissolved (Anderson, 2002). Diffusion requires little or no energy because molecules are always randomly moving; this is due to their kinetic energy. Diffusion occurs only when there is an imbalance in the areas of concentration. The difference in concentration of molecules over a distance is known as a concentration gradient (Enger, Ross, & Bailey, 2005). Furthermore, net movement relates to the movement of molecules in one direction minus the movement of molecules in the other direction. Finally, if movement in one direction equals movement in the other direction then dynamic equilibrium occurs (Enger, Ross, & Bailey, 2005).

The diffusion of water molecules across a selectively permeable membrane involves a special form of diffusion called osmosis. When the external and internal solute concentration are equal, there is no movement of water will be observed. This is described as isotonic. Osmosis does not occur in an isotonic solution, because the concentrations are equal on both sides of the membrane and there is no net movement of molecules from one side of the membrane to the other (Payne, 2007). A hypotonic solution is a solution in which the concentration of dissolved substances is lower than the concentration inside the cell (Payne, 2007). If a cell is put into a hypotonic solution, osmosis will cause water to move from the through the cell membrane into the cell. A solution is hypertonic if its concentration of dissolved substances is greater than the concentration inside the cell (Payne, 2007). If a cell placed in a hypertonic solution, it will lose water. Water molecules will always move from a hypotonic region to a hypertonic region (Marieb, 2004). In osmosis, a selectively permeable membrane allows passage of water molecules but prevents the passage of most other molecules. By contrast, a permeable membrane allows passage of most molecules whereas an impermeable membrane prevents passage of most molecules. An example of a selectively permeable membrane is dialysis tubing, which removes toxins from the blood of dialysis patients while returning cleansed blood. The rate of osmosis depends on such variables as the concentration of the solute, the temperature of the solution, and the osmotic pressure exerted on the membrane separating the solution from the solvent.

The purpose of this experiment was to demonstrate diffusion of glucose through a semi-permeable membrane, in this experiment, dialysis tubing; and measure the starting and ending weights of six prepared dialysis tubes and compare the results to determine the effects of osmosis with varying concentrations. For the diffusion demonstration, the glucose will travel from within the dialysis tubing (high glucose concentration) to the solution of potassium iodide (low concentration of glucose). For the experiment of osmosis including the six prepared dialysis tubes, the ending weight of each sample will increase with increasing concentration.

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Materials and Methods:

Materials for diffusion demonstration:

Hand out from the Natural Science Establishment, dialysis tubing, beaker, distilled water, potassium iodide, glucose indicator strips, paper towels, graduated cylinder, razor blade, and a prepared solution of glucose/starch.

Procedure:

Working in a group of four, we knotted one end of the dialysis tubing and filled it with 15 ml of the prepared glucose/starch solution. We then dipped a glucose indicator strip into the tubing to verify the presence of glucose. The open end of the tubing was then knotted and the tubing dried by lightly patting it with a paper towel. The beaker was then filled partially with distilled water; 1 ml of potassium iodide was then added, and the solution was tested for the presence of glucose. This data was recorded in table 1 on the data sheet along with the starting color of both the potassium iodide solution and the glucose/starch solution. The dialysis tubing was then submersed into the beaker containing the potassium iodide solution, and set aside for 30 minutes to allow maximum diffusion.

After the 30 minutes, the color was observed and recorded on the data sheet. The dialysis tubing was removed from the beaker and a small slice was made, we then used a glucose indicator strip to test for the presence of glucose, along with the solution in the beaker. The results were then recorded in table 1on the data sheet.

Material for osmosis experiment:

Hand out from the Natural Science Establishment, six dialysis tubing, six plastic cups, distilled water, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M samples of a sucrose solution, paper towels, and a scale.

Procedure:

Six plastic cups were obtained and labeled 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. Next, each of the six dialysis tubes were knotted on one end and filled with the sucrose samples, and then tied off. These samples were then dried by patting with a paper towel, weighed and placed into their corresponding cups. The mass of each sample was recorded in table 2 on the data sheet. Each cup was then filled with distilled water so that the dialysis tubing was fully submersed. These were then set aside for 30 minutes to allow maximum osmosis to occur.

After the 30 minutes, each sample was removed from the water and thoroughly dried. A final weight was taken and recorded in table 2 for each sample on the data sheet.

Results:

Table