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Introduction

G.C.S.E Science: Investigating the effect of Sucrose Concentration on the Rate of Osmosis in Potato Chips Sophie Chapman 25th March 2003 Aim: I shall carry out a sequence of independent experiments in order to investigate how the rate of osmosis in a potato chip is affected when the concentration of sucrose solution is varied. Apparatus: 300ml Sucrose concentration 300ml Distilled Water 2 x 100ml beaker 1 x 100ml Measuring Cylinder 1 x Potatoes 1 x Forceps (Tweezers) 1 x Scalpel Chipper 12 x Polystyrene Cups 1 x Stop - clock Tissues 12 x Sticky Labels 1 x Pen 1 x Calculator 1 x Ruler (measuring mm) 1 x Balance 1 x Polythene Food Bag Cardboard Apparatus Justification: To complete the experiment, I need 300ml distilled water and 300ml sucrose concentration as I intend to carry out 12 tests (using 6 different volumes but each shall be repeated twice) each using a 100ml of liquid whether it be pure water, pure sucrose concentration or a solution containing both. I will detail about the exact volumes of water and sucrose concentration that I want to use in each experiment, in the written procedure. I shall use varied amounts of sucrose solution for each test in order to adjust the concentration - a solution containing more sucrose has a greater concentration than a solution containing less sucrose solution. It is essential that the concentrations be varied throughout the investigation for I am analysing the effect of sucrose concentration upon the rate of osmosis in potato chips. Distilled water is required to reduce the concentration of the sucrose solution. I shall use distilled water as opposed to tap water because it is de - ionised and contains fewer impurities therefore is unlikely to contaminate the experiment and affect the results achieved. I have chosen to use a measuring cylinder that can measure out 100ml of liquid without having to constantly refill a smaller measuring cylinder (such as a 50ml one) ...read more.

Middle

The cell membrane in each potato cell is said to be partially permeable. Osmosis is a special type of diffusion involving water molecules. It happens when a partially permeable membrane separates two solutions. In this experiment, the partially permeable cell membrane of the potato chip cells will separate the water in the potato chip from the solution it is immersed in, either pure, distilled water or a solution of sucrose concentration. Osmosis is the crossing of water molecules from a weaker solution into a stronger solution through a partially permeable membrane. A solution is a solute dissolved in a solvent. The solution in this investigation is sucrose concentration. It is a solution because the sugar, which is a solute, is dissolved in water, which is a solvent. The diagram shows that the weaker solution contains fewer sugar (solute) particles than the stronger solution which has a higher sucrose concentration. If the sugar and water particles were added up together, those in the weaker solution would make up a larger fraction or proportion of the total, than in the stronger solution. This means that the weaker solution will have a higher concentration of water molecules than the stronger solution. If the selectively permeable membrane was removed, the water and sucrose particles would move from one side to the other. This is called diffusion. As there is a greater concentration of water in the weaker solution, the water molecules usually diffuse into the stronger solution and the sucrose particles would move from the stronger solution to the weaker. If there is a barrier that is a selectively permeable membrane which only allows water molecules pass through it, the result is that only water moves - from the weaker solution to the stronger solution. This process is called osmosis, the solute particles are unable to diffuse from the stronger solution to the weaker one because the particles are too large to pass through the membrane. ...read more.

Conclusion

It was extremely difficult, as there were only two people per group, to drop 6 chips into 6 separate cups as well as start the stop - clock all at the same time. Theoretically, the potatoes were not immersed into the solutions for exactly the same times which means that osmosis might have continued for longer in some cups and shorter in others. Therefore, if I was to do the experiment again and had more time, I would like to use 6 separate stop - clocks and (for each experiment) begin one experiment first and then begin the next with another stop - clock ten minutes later and so on. This idea would have assured that the experiment remained fair throughout and osmosis occurred for exactly the same duration of time for each experiment. The results show that a larger concentration gradient means that there is a greater difference between the water concentrations inside and outside of the potato cells. Likewise a smaller concentration gradient means that the difference between the water concentrations inside and outside of the potato cells is small also. I did not monitor the temperature during the entirety of the investigation but instead assumed that the temperature was approximately room temperature (37o C). I doubt there would have been a dramatic difference nevertheless. Another group measure the temperature and their results were ever so slight therefore I don't think this is essential because the change in air temperature would have been greater than the temperature of liquid. As the air temperature was so small, the liquid temperature would have been lower and therefore this didn't affect the results. In order to extend my knowledge of osmosis, I could investigate the concentration of sugar in other vegetables such as carrots, parsnips, turnips etc. I would repeat the same procedure but I would take into account the problems I cam across and use the solutions offered in the evaluation. This would be an interesting investigation because it could then lead to being able to compare the rates of osmosis in different vegetables when affected by the concentration of sucrose solution. ...read more.

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