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Investigation to find the effect of different concentrations of sugar Solutions on osmosis.

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Introduction

Investigation to find the effect of different concentrations of sugar Solutions on osmosis. Introduction Osmosis is the diffusion of water molecules from a place where they are in a higher concentration (such as a dilute sugar solution), to a place where the water molecules are in a lower concentration (such as a concentrated sugar solution) through a semi-permeable membrane. Dilute Sugar Solution Concentrated Sugar Solution Water movement This is a diagram to illustrate a concentrated sugar solution, separated from dilute sugar solution by a membrane. The membrane had pores, which are very small. The water molecules are small compared to the sugar molecules. The pores are big enough to let the water molecules through but not the sugar molecules. It is called a semi-permeable membrane because it will let some molecules through but not others. The water molecules will move from the left-hand-side to the right-hand-side from an area of high concentration of water to a low concentration of water. Factors affecting osmosis * Concentration of external solution * Volume of external solution * Type of external solution * Surface area of tissue * Type of tissue * Mass of tissue Independent Variable In this experiment I have chosen to change the concentration of the external solution throughout the experiment. I will do this by changing the amount of water and slat solution each time as in the table below: Water (cm ) ...read more.

Middle

Then weigh each one and record which weigh of potato is going into each solution. 3. Put three potato cylinders into each boiling tube and place coloured drawing pins on to two of them so they can be identified, stopper on top and leave for 48 hours. 4. After 48 hours take each potato out of its boiling tube one at a time and weigh it and record its mass beside which it was before the experiment. 5. Work out the calculations to find the average difference in mass. Safety * Tie hair back * Tuck in stool * Careful when handling solutions * Use apparatus safely * Place bags under desk * Wash hands after using solutions * Be careful when handling blade Equipment * 5 boiling tubes * potato * boiling tube rack * 5 stoppers * weighing scales * water * salt solution * potato borer * measuring cylinder * coloured drawing pins * blade Results See previous page Conclusion The evidence obtained from this investigation supports the prediction I made. I found that as you increase the concentration of the salt solution the change in mass decreases. Therefore if you decrease the concentration of the salt solution, the change in mass increases. For example the mass of the potato in the 0.8 salt solution had an average of -0.05 decrease, whereas the mass of the potato in the 0.2 salt solution had an average increase of 0.06 after 48 hours. ...read more.

Conclusion

The smaller the concentration of water in the external solution the greater amount of water that leaves the cell. Evaluation During my experiment I used coloured drawing pins to identify each piece of potato, this was so I knew which potato I put in first to make it a fair test. If I were to do the experiment again I would use pipettes which consist of smaller volumes, instead of measuring cylinders to measure out the solutions as this would give me more accurate results. I think my results are quite accurate but I do think there is room for improvement. I could improve my results by repeating the experiment. I may repeat it four or five times more and this would then give me a more accurate average. I would also again use pipettes instead of measuring cylinders. Also instead of my percentages of salt solution going up in twenty's, I would go up in five's. There is a smaller range so therefore I could more accurately pinpoint the exact position where the potato starts to lose water. For example my isotonic point is 20% but if I used a smaller range of percentages I could actually find that it could be 17% From my graph I can see that I have two anomalies. This may have been due to the fact that the pieces of potato were not thoroughly dried out. Finally I would repeat the experiment to see if I were to find the same results. ...read more.

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