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An investigation into the effect of Sucrose concentration on osmosis

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Introduction

AIM: The aim of my experiment is to investigate the effect of sucrose solution on osmosis in potato cells, and what the point of equilibrium would be. I shall be observing how the mass of the potato chip changes in five different concentrations of glucose solutions. HYPOTHESIS: Osmosis is the diffusion of water molecules from a high water potential to a lower water potential through a partially permeable membrane. A partially permeable membrane, such as a cell wall, allows small molecules, such as water molecules, pass through it, but does not let bigger molecules such as sucrose through it. Cells placed in distilled water take up water by osmosis. This happens because the cell contains dissolved chemicals and therefore has a lower water potential than the distilled water surrounding it. As there are more water molecules outside the cell, more go in to the cell than out of it. The net movement of the water molecules is into the cell, and the cell will increase in mass. Eventually the cell stops taking up water, even though the concentrations inside and outside are not even. This is because the cell wall becomes stretched and prevents any more water entering. The cell is said to be turgid. Cells placed in a concentrated sugar solution lose water by osmosis, as the water potential is higher inside the cell. As there are more water molecules inside the cell, more water molecules leave the cell than enter it. The net movement of the water molecules is out of the cell. ...read more.

Middle

Lastly, I shall use the same volume of solution for each test tube. The potato cylinders must be totally covered in the solution, and the amount of solution will be kept the same, as all the potato cylinders are the same size. In my pilot study, I found that 20cm� of solution is a suitable amount for this experiment. This is because 10cm� of solution only just covered the potato cylinder, whereas 20cm� covers it fully and has space left over. This number is also easy to make solutions of different concentrations from. I chose to do these concentrations of sugar solution: 0.0M 0.7M 0.2M 1.0M 0.5M This is because in my pilot study, I found that my point of equilibrium was close to when the concentration was 0.2M. I tried to make my concentration fairly evenly spaced, so that I would get a good line on my graph. The mass of the potato cylinders is a dependent variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams, measuring to 2 decimal place, using a digital balance so my results will be precise. The potato cylinder will be weighed before it is put into the solution, and after. This will allow us to whether osmosis has taken place, and to what extent. To make my experiment as reliable as possible with the amount of time given to carry it out, I shall repeat this experiment once and use the average of these results for my graph. ...read more.

Conclusion

* I cut all the potato cylinders uniformly with an apple corer, therefore all the side were the same length. * I left all of the potato cylinders in their test tubes of sugar solution for exactly 25 minutes each; therefore they all had the same amount of time for osmosis to take place. * I used the same volume of solution for each test tube. Some further work I could do to help me find out more exactly what the point of equilibrium is, is to do this experiment again, however instead of measuring the increase or decrease in mass of the potato, I would measure the change in length of the potato cylinder. Then I would plot the results for that experiment on the same graph I drew for this experiment. Hopefully, the point of equilibrium would pass at the same point on the x-axis, however if it didn't, I would average out the two points of equilibrium and use that answer for my point of equilibrium. Table of Results Concentration (M) Try 1 Try 2 Average % change in mass Mass before (g) Mass after (g) Change in mass (g) %Change in mass (g) Mass before (g) Mass after (g) Change in mass (g) % Change in mass 0 5.46 5.62 0.16 2.93% 5.26 5.48 0.22 4.18% 3.56% 0.2 5.45 5.52 0.07 1.28% 5.27 5.34 0.07 1.33% 1.31% 0.5 5.36 5.28 -0.08 -1.49% 5.36 5.3 -0.06 -1.12% -1.31% 0.7 5.37 5.2 -0.17 -3.17% 5.14 4.94 -0.2 -3.89% -3.53% 1 5.41 5.16 -0.25 -4.62% 4.97 4.69 -0.28 -5.63% -5.13% Aditi Gupta LVM ...read more.

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