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Skill Area P: Planning

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Introduction

Skill Area P: Planning Aim: The aim of the experiment is to investigate the effect of concentration of a certain salt solution on the amount tissue of potato slices. Osmosis is the movement of a solvent (e.g. water) through a semi permeable membrane, from a solution that has a lower concentration of solutes (e.g. salt) to one that has a higher concentration of solutes. In osmosis, the membrane does not allow the solute to pass through, but does allow the solvent to pass through. The rate in which osmosis occurs depends on the temperature of the solution, the concentration of the solute, and the electrical charge of the solute. Another factor is the difference between the pressures that both sides of the solutions exert onto the membrane. Osmosis stops when the two solutions are equal in concentration. Prediction: For this investigation I think that the lower the concentration of the salt solution the larger the mass of the potato will be at the end. This is because the water molecules pass from a high concentration (solution) to a low concentration (potato). As a result the potato in lower molar concentrations will gain a larger mass than in higher molar solutions. To create a fair test variables of the experiment will have to be kept the same whilst only one variable is changed. ...read more.

Middle

5. Using a pipette and pipette I measured out different amounts of salt solution and distilled water which I then put into the test tubes in a percentage ratio giving me the various molar concentrations. 6. I put 3 potato slices into each beaker and then sealed the tubes. I sealed the tubes to prevent anything from getting into them and also to stop water from evaporating 7. Whilst waiting I drew up a basic table for my results. 8. After 25 hours I drained out the solutions in the sink and placed all the slices on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which slice came from which solution. 9. I dried each slice with the paper towel and then placed each one on the scales so that I could weigh them. I recorded the weights and put them in the table with the previous results. Results: Molarity Mass Before (g) Mass After (g) Change in Mass % Change 0.00 1.72 1.85 0.13 7.5581 1.64 1.89 0.25 15.2439 1.63 1.85 0.22 13.4969 Average 1.66 1.86 0.20 12.0996 0.25 1.56 1.46 -0.10 -6.4102 1.66 1.64 -0.02 -1.2048 1.51 1.15 -0.36 -23.8410 Average 1.58 1.42 -0.16 -10.4853 0.50 1.65 1.45 -0.20 -12.1210 1.66 1.52 -0.14 -8.4337 1.88 1.71 -0.17 -9.0425 Average 1.73 1.56 -0.17 -9.8657 0.75 1.64 1.36 -0.28 -17.0730 1.49 1.34 -0.15 -10.0670 1.87 ...read more.

Conclusion

This way would have allowed me to get more accurate results and would have allowed me to produce a more detailed graph. The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato, I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. I could also weigh each slice on a more accurate scale, e.g. not to 0.00g but to 0.0000g. There was only one anomaly and this may have been caused by me. When the potato slices were removed from the test tubes and dried I may well have dried some potatoes more thoroughly 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 time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction. ...read more.

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