The Effect of Solute Concentration Upon the Rate of Osmosis
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The Effect of Solute Concentration Upon the Rate of Osmosis Aim To investigate the effect of changing the concentration of sugar solution on the amount of osmosis taking place between the sugar solution and a potato cube with a specified size. Introduction If a higher concentrated solution of water is separated by a semi permeable membrane from a lower concentrated solution of water, the water will move to the lower concentrated area of water so that it can create an equilibrium-like state, in which the concentration of water on both sides of the membrane are the same. The semi permeable membrane will allow smaller molecules such as water, carbon dioxide and oxygen through it, but will not allow larger molecules such as sugar molecules through. Osmosis can be compared to diffusion, where the higher concentrated particles will attempt to spread themselves around so that the whole area they are in will have a balanced amount of that particle. Osmosis is very important because it does not require energy for plants to take up in their roots, therefore it is not a form of active transport, which will help plants to grow. Approach I have decided to investigate the rate of osmosis in a potato, because I already have the molarity of sucrose within a potato, 0.27m, which I found in a textbook written by M.B.V Roberts. The basic idea is that I will put potatoes all of which are the same surface area into different concentrations of sucrose solution, and view the osmotic effects of doing this. Factors That Affect the Rate of Osmosis Temperature: increase of temperature speeds up most reactions, therefore a change in speed would increase the rate in osmosis.
If I did do these all at the same time, I will probably not be able to weigh them at the right time, because as I am weighing one group of the potatoes, it would time to weigh another, and the experiment would go wrong. Results Molarity of solution (mol/dm³) Mass of potato cube (g) Mass After 10 mins (g) Mass After 20 mins (g) Mass After 30 mins (g) Mass After 40 mins (g) 0 0.84 0.84 0.85 0.85 0.86 0 0.76 0.77 0.78 0.77 0.8 0 0.89 0.96 0.97 0.97 0.98 0 0.79 0.88 0.84 0.86 0.88 Molarity of solution (mol/dm³) Mass of potato cube (g) Mass After 10 mins (g) Mass After 20 mins (g) Mass After 30 mins (g) Mass After 40 mins (g) 0.2 0.63 0.59 0.58 0.55 0.6 0.2 0.54 0.56 0.56 0.54 0.58 0.2 0.58 0.59 0.59 0.56 0.62 0.2 0.53 0.55 0.56 0.54 0.53 Molarity of solution (mol/dm³) Mass of potato cube (g) Mass After 10 mins (g) Mass After 20 mins (g) Mass After 30 mins (g) Mass After 40 mins (g) 0.4 1.71 1.86 1.86 1.78 1.73 0.4 1.55 1.62 1.63 1.59 1.5 0.4 1.26 1.25 1.24 1.22 1.23 0.4 1.14 1.14 1.31 1.12 1.09 Molarity of solution (mol/dm³) Mass of potato cube (g) Mass After 10 mins (g) Mass After 20 mins (g) Mass After 30 mins (g) Mass After 40 mins (g) 0.6 0.59 0.59 0.6 0.52 0.53 0.6 0.58 0.59 0.57 0.52 0.52 0.6 0.62 0.55 0.54 0.53 0.51 0.6 0.54 0.59 0.57 0.54 0.51 Molarity of solution (mol/dm³) Mass of potato cube (g)
Another problem is trying to cut potato squares into the same sizes. I accidentally cut them into slightly different sizes, which meant that the rate of osmosis can be higher due to a larger surface area of the potato. I seem to have some anomalous results where I would have expected the mass to go down when it has gone up and the other way round. As far as I can tell this could be due to me over drying one piece of potato or forgetting to dry it at one point. This made a lot of difference to the results graph. I believe that the line of the graph didn't cross 0.27 because I didn't have enough results to make it accurate enough. For example taking the mass of the potato more often than every 15 minutes, say every 5 minutes would make it a great deal more accurate. But this way I would have to think of another way to take reading for the potato, I would have trouble weighing 6 at once. Rate of reaction from these results wasn't quite what I expected, the difference in rate of osmosis was not as great I had hoped and the anomalous result made things look very odd on the graph but overall the experiment was as I planned and I got the results I wanted. I could have furthered this experiment by taking more frequent results, for example, every 5 minutes, and I could have weighed the potatoes until they had been in the solution for a longer time, to find out how long it will take for the potato squares to be in a state of equilibrium.
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