Osmosis and Weight of Potato Sticks - Essay Example

Osmosis Background Osmosis is the movement of water through a semi-permeable membrane, from a region of higher water concentration to one which has low water concentration. Alternatively, it is the diffusion of water from a solution that has lower concentration of solutes to the region where there are more solutes. The concentration of a sugar solution will increase with more sugar molecules, and this concentration is expressed as molarity. The higher molarity means more sugar solutes or more sugar molecules in the solution. A partially permeable membrane is one where the size of the molecules entering or exiting can be controlled depending on its pore size. There are artificial semi-permeable membranes and naturally occurring membranes. Artificial semi-permeable membranes are dialysis tubings (e.g. Visking tube), and while natural membranes are those found in the cell walls of plants and plant organs. The potato tuber is composed of cells that are bounded by semi-permeable membranes that permit the entry and exit of selected biomolecules. Within the cells can be found different solutes like ions, sugars, proteins and water. Among these compounds water is the most plentiful because it serves as the medium where the solutes are suspended or dissolved. When a potato slice or chip is immersed in water, the potato chip will increase in size or swell because the water from the outside (which has higher concentration) will enter the potato cells. This will continue until the osmotic concentrations of the potato and the water in the external environement are in equilibrium with one another. The cells will swell, meaning that there will be an increase in the volume, and there will also be increase weight due to more water. On the other hand, if the potato is placed in a solution with a very high concentration of sugar, then it is projected that the potato will become smaller or lighter because the water in the cells of the potato will diffuse out of the potato cells into the solution. This will result in a dehydrated potato. The hypothesis being tested in this experiment is: potato sticks immersed in sugar solutions will exhibit decreased weights and length commensurate to the increase in the sugar concentration due to osmosis. Aim: To measure changes in the weight of potato that have been submerged in sugar solutions of different concentrations. Methodology Different weights of sugar were added to make the following solutions: 0.2 M (molar), 0.4M, 0.6M, 0.8M and 1M. Six ml of the solutions were places in test tubes. Then potato sticks were cut from the same potato tuber, and were weighed to get their initial weights. The potato sticks were then placed in the test tubes that contained the sugar solutions. The tubes were placed in test tube racks to allow for osmosis and equilibrium to occur. After thirty minutes, the potato sticks were taken out of the solution and weighed again. The length of the potato sticks were also determined. Results and discussion Table 1 presents the observations taken from the experiment. The difference in the initial weight and the weight after the sticks were immersed shows that there was a decrease in the in the weight commensurate to the increase in sugar solution. This can also be seen in the presentation of the results in Figure 1. Therefore, as the sugar solution increased, there were more water molecules leaving the potato cells towards the exterior environment (Figure 2). Thus, more water molecules leave the potato when there is more sugar in the external solution. However, it can also be seen in Figure 3 that the lengths of the sticks were increased under increasing sugar concentration. This is in contrast to the expectation that the sticks should be decreasing because the water from the potato will leave the cells, and this should result in the decrease inthe length. A possible source will be error from the cutting of the potato sticks, the incorrect use of the cutters and the erroneous measurement of the length. Table 1. The raw data on the observations taken from the experiment. Concentration of sugar solutions (Molar) Length of Potato Stick (mm) Initial weight of potato stick (grams) Weight of potato sticks after 30 mins (grams) Difference in Weight (grams) 0.2 48 4.38 4.31 -0.07 0.4 49 4.49 4.27 -0.22 0.6 51 4.62 4.27 -0.35 0.8 53 4.47 4.02 -0.45 1 47 4.46 4.09 -0.37 Figure 1. The effect of increasing concentrations of sugar on the changes in the weight of potato sticks Figure 2. Decrease in the weight of potato sticks immersed in different concentrations of sugar solutions. Figure 3. The effect of increasing concentration of sugar solutions on the length of potato sticks Conclusion The results of the experiment showed that osmosis did occur based on the changes in the weights of the potato sticks. The experiment gave a correct illustration of how osmosis works. However, the results taken from the lengths were not reliable. Therefore, if the experiment is repeated, more care will be given in the measurement of the different variables. Read More