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Investigation to see how Concentration affects the rate of Osmosis on Potatoes.

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Introduction

Investigation to see how Concentration affects the rate of Osmosis on Potatoes Planning The aim of this investigation is see how altering the rate the concentration of water and salt solution affects the rate of osmosis of potatoes. Osmosis is the diffusion of water from a high concentration of water (a dilute solution) to a low concentration of water (a concentrated solution) through a semi-permeable membrane. A semi-permeable membrane is porous but allows water to pass through it more rapidly than dissolved substances. The diagram shows how water molecules have diffused from a dilute solution to a concentrated across a semi permeable membrane. As a result, the level of liquid on the left will rise, and fall on the right. The rate of osmosis is dependant on a few things. It depends on * The thickness of the membrane * The concentration inside and outside the membrane - Concentration gradient * The size of the ions * The Surface Area. Using potato cylinders and 1M Salt Solution (NaCl Solution). I will look at the rate of osmosis on the potato cylinders in different concentrations of salt solution. I will dilute the solutions using distilled water. Hypothesis I predict that when the potato tubes are in a higher concentration of the salt solution than the concentration of water, i.e. the solution is concentrated, then the potato tubes will lose mass and become smaller. This is because the concentration of water outside the potato cylinders is concentrated, and there is not much water. Due to osmosis the water inside the potato cylinders will move out. This will decrease the mass of the potato, make it smaller and make it flaccid due to the loss of water. The potato cells lose turgor and become flaccid. I predict that when the potato tubes are in a lower concentration of the salt solution than the concentration of water, i.e. ...read more.

Middle

because there were not enough test tube racks * I did repeat the experiment but the second time the results had to be taken at a different time period - only after 2-3 hours due to time. The first experiment results were taken after about 18 hours, which is why the results in Experiment 2 may be anomalous. * The same apparatus could not be used as the experiment was done after a few days. * The same temperature could not be kept as the room temperature differed from experiment 1 to 2. Precautions These are the safety precautions that were carried out to ensure that the experiment was safe: * The scalpel and cork borer was used to cut the potato on the white tile, so nothing is damaged * The tubes were kept in a beaker so that the tubes could not be tampered with * They were left untouched so the results would not be affected * The beaker of test tubes was put near the wall, on the desk so that the tubes would not fall of the desk. Here are the results tables for Experiment 1: Results Mass of Potato cylinders / g Tube 1 2 3 Averages 1 0.73 0.71 0.68 0.71 2 0.68 0.67 0.69 0.68 3 0.74 0.73 0.83 0.76 4 0.77 0.82 0.73 0.77 5 0.96 0.93 0.96 0.95 6 0.88 0.92 0.96 0.92 Before After Mass of Potato cylinders / g Tube 1 2 3 Averages 1 0.90 0.86 0.84 0.86 2 0.95 0.83 0.91 0.89 3 0.92 0.95 0.92 0.93 4 0.90 0.86 0.93 0.90 5 0.91 0.97 0.84 0.91 6 0.83 0.85 0.89 0.86 Gain or Loss Tube Change in Mass / g 1 -0.15 2 -0.21 3 -0.17 4 -0.13 5 0.04 6 0.06 (A negative number indicates loss) Here is the results table for Experiment 2: Before After Mass of Potato cylinders / g Tube 1 2 3 Averages 1 0.65 0.82 0.72 0.73 2 0.83 0.73 0.79 0.78 3 ...read more.

Conclusion

If the temperature were kept constant then the experiment would be fairer and give better results. This could have been done by doing the experiment in a temperature-controlled room, to ensure that the temperature remains constant. The experiment could also have given better results if I had used more accurate weighing scales, to give better weight readings. If I were to repeat the experiment I could have possibly found a machine to cut the potatoes. This would ensure that all potatoes would be the same weight and dimensions and make the experiment fairer and give better results. To find better results, I could also have measured the volume of the solution left when re weighing the potatoes. If this was done, then I could have seen if the volume changes match the mass changes. It would also have provided extra evidence for the accuracy of the results. In these ways I could have improved my current experiment I carried out. To extend my experiment I could test how concentration affects the rate of osmosis on different vegetables. I could have used different vegetables, like a cucumber. Then I could find out whether osmosis occurs with the same trends with any vegetable. I could also have done the experiment with another solution instead of salt solution. I could have used sugar solution, and then compared the two sets of results to see if it makes a difference and why it makes a difference. I could also have extended this experiment by testing more solutions with the potato cylinders. I could have used more different concentrations of salt solution to give better results in this experiment. By doing this I could have found the isotonic point, which is where osmosis is balanced so there is water movement, as the water concentration is the same on both sides of the semi permeable membrane. I cold also have tested how the osmosis rate changes with different potato cylinder sizes. From this I would be able to see if the size of the potato affects the rate of osmosis. Ricky Patel ...read more.

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