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osmosis coursework

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Osmosis investigation

Aim: to investigate the affect of using different amounts of sugar solution and to measure the osmotic reaction when different amounts are put on a small potato chip.

Intro: we were told that we were going to be doing an investigation in to osmosis as our coursework, osmosis is a process involving molecules and a semi-permeable membrane from a place of higher concentration of molecules to a place of lower concentration of molecules until the concentration on both sides is equal. To find out about osmosis we did an experiment involving putting equal bits of potato chip into some different solutions of water and sugar–solution and see what affect it had on the potato after a certain amount of time. We also had to think about things which would affect the experiment and the ideas we came up with were size of chip, temperature and types of potato.  

Hypothesis

Wikipiedia define osmosis as “the net movement of water or any other solution as molecules from a region in which they are highly concentrated to a region in which they are less concentrated.” This movement must take place across a semi-permeable membrane, which lets smaller molecules like water through but does not allow bigger molecules to pass through e.g. sugar. The molecules will continue to move in and out until the area in which the molecules are found is equal.

For this particular investigation I think that the lower the concentration of the sugar solution in the beaker the larger the mass of the potato will be. This is because the water will pass from a high concentration, (in the water itself) to a low concentration, (in the potato chip). Therefore, the chips in more water will have a larger mass than in higher sugar solution.

Method

  • cut up equal sizes of potato and weigh them out and make them as equal  weight as possible
  • put the weight of the potato chip in a table (you’ll need them later)
  • measure out 5 solutions 100% water / 0% sugar solution

                                                 75% water / 25% sugar solution

                                                 50% water / 50 % sugar solution

                                                 25% water / 75 % sugar solution

                                                 0% water / 100% sugar solution

  • put the potato chips in at the same time and leave them in there for an hour
  • take the potato chips out and weigh them again on the same scales
  • put down the new weights on a table  

Table of results

Moles of sugar solution

Before mass grams

After mass grams

change

Change in %

Average %

0

1

0.67

0.78

0.11

16

15.66

0

2

0.61

0.71

0.10

16

15.66

0

3

0.71

0.82

0.11

15

15.66

0.25

1

O.61

0.70

0.09

15

18.00

0.25

2

0.59

0.70

0.11

19

18.00

0.25

3

0.55

0.66

0.11

20

18.00

0.5

1

0.62

0.65

0.03

5

8.66

0.5

2

0.63

0.71

0.08

13

8.66

0.5

3

0.61

0.66

0.05

8

8.66

0.75

1

0.58

0.56

-0.02

-3

-0.33

0.75

2

0.61

0.60

-0.01

2

-0.33

0.75

3

0.66

0.66

0

0

-0.33

1

1

0.70

0.64

-0.06

-9

-12.66

1

2

0.71

0.68

-0.09

-13

-12.66

1

3

0.75

0.63

-0.12

-16

-12.66

Table/graph

(What did I find out?)

My graph gives the line of best fit for the change in mass of the potato chips over the course of the experiment. There is a pattern on my graph and this is that as the amount of the solution increases, the change in mass decreases. The graph goes down on a steep gradient but I think that the line will eventually even out, I think this because the potato chip will eventually becoming as flaccid as it possibly can. The line of best fit that has been put in, you can see that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable apart from the second one, this might of happened because of one of the variables we have previously discussed might have happened. My graph fits in with my prediction which I made.

Evaluation

The experiment was very successful in my opinion. I got a large quantity of very accurate results from which I was able to create a good graph. I think I took enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results for example 0.10m, 1.15m, 1.20m e.g. This way it would have allowed me to find out the isotonic point

The cutting of the potatoes was the most difficult part of the experiment because I was recording my results by mass; it could have affected the surface area and the overall rate of osmosis. If I were to repeat the experiment I would have possibly (if there is such a thing) found a machine to cut the potato as it would make sure that all the potatoes would be the same weight and size. As well as the potato I could have found a more accurate way to measure out the solutions, if I could do this it would make sure that I have an accurate amount of liquid in each beaker. I could also weigh each chip on a more accurate scale for example not to 0.00g but to 0.0000g if I had a better set of scales.

There was not any out of the ordinary results, but one was not as close to the line as the others. This may have been caused by myself or my partner.  This may have been when the potato chips were removed from the beakers and dried I may well have dried some potatoes more than others this might make some 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 the potatoes were dried in the same way for the same time. However I think that the experiment was successful and I was pleased with my results and with my prediction. us

Conclusion

Because water molecules have kinetic energy, they are constantly moving around as a liquid. The greater the concentration of water molecules in a solution, the greater the total kinetic energy. This means that as the concentration of sugar is increased in a solution, the concentration of water decreases, loosing some of the solution’s water, and decreasing its ability to move between solutions by osmosis. Relating this to the potato chip, as the concentration of sugar in each solution was increased, the water in that solution can not move easily to the potato, causing water from the potato to move to the solution, decreasing its size and weight. This would explain why potato chips put into a solution of 0 molar seemed very stiff compared to the potato chip used for 1 molar which went all soft.

In conclusion I can say that the movement of water through semi permeable membrane of a potato is affected by concentration of sugar solution. The higher the concentration of glucose solution, the more the potato chip will lose its weight and size.

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.

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