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How does Concentration affect the Rate of Osmosis in Potato Cubes?

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Introduction

How Concentration affects Osmosis By Bonnie Kingett Contents Aim.............................................................................................................................................2 Background Theory....................................................................................................................2 Safety Precautions.....................................................................................................................2 Method.......................................................................................................................................3 Preliminary Experiment..............................................................................................................3 Final Method..............................................................................................................................4 Results.......................................................................................................................................4 Graph.........................................................................................................................................4 Conclusion.................................................................................................................................6 Evaluation..................................................................................................................................6 Aim The purpose of our experiment is to find out how the concentration of a sugar solution affects osmosis in a cube of potato. We will then plot a graph of our results, and interpret them in order to find out which concentration affects the weight of the potato cube the most. Background Theory Osmosis (from the Greek word 'to collide' or 'to hit') is the movement of water through a partially permeable membrane (i.e. a piece of Visking tubing) from a lower concentration to a higher concentration. In the diagram below, the blue circles represent water (H2O) molecules, and the orange rimmed ones represent sugar (C12H22O11) molecules. The dotted line represents a piece of Visking tubing, and the red arrows show the direction of the water molecules. The reason that water can travel through the partially permeable membrane is that there are tiny gaps between the cells in the membrane. For example, in the diagram below, we can see water molecules (the aqua circles) ...read more.

Middle

- Then, take three lots of 5ml of the water, and put them into the last remaining test tubes. Repeat, but with Sucrose, to make the overall amount of liquid up to 10ml. - Drop one potato cube into each tube, and start the timer when the last piece of potato is in its tube. Wait twenty minutes, then carefully tip away the excess liquid in each tube, but make sure that the potato is still intact. - Write '0' on one paper towel, '0.5' on the next and '1' on the last. Then, blot the potatoes on their respective towel, depending on what molarity they were soaked in. Weigh them again, and calculate the weight difference by using the formula: Final Weight - Initial Weight = Weight Change We can now estimate from this table roughly where our results should be about when we conduct our final experiment. Final Method We decided, for our final method, to increase the range of our results. Instead of using molarities of 0, 0.5 and 1, we chose to experiment with 0, 0.2, 0.4, 0.6, 0.8 and 1. Someone suggested leaving out the first and last, since we completed them in our preliminary experiment, however we repeated them in case of temperature change and other uncontrollable factors. ...read more.

Conclusion

The cutting of the potatoes was the most difficult part of the experiment. Although I was recording my results by weight, it could have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have found a way to make sure all of the chips were the same dimensions, like by using a cutter. As well as the potato, I could have found a more accurate way to measure out the solutions and to determine the molar concentrations, like by using a burette. This would ensure that I have an accurate amount of solution in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.000g. There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by human error. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same accuracy. ?? ?? ?? ?? 1 ...read more.

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