In this coursework I am going to investigate the factor how different concentrations of sugar solutions will affect the rate of osmosis on a potato cylinder,

Apparatus

• 3 test-tube racks
• 6 boiling tubes
• 1 Cork borer
• Large potatoes
• Potato peeler
• Paper towels
• 5 different concentrations of sugar solution. (0.0 pure distilled water, 0.1, 0.2, 0.4, 0.5, 1)
• Ruler
• Weighing scales
• Blunt knife
• 10cm3  measuring cylinders
• Cotton wool/corks
• Stopclock/Watch

Note: Instead of using a measuring cylinder I am going to use a Burette, which will make my results more accurate.

Safety

As this experiment is relatively safe, there are no major safeties precautions that I will need to apply. However, I will not touch the potato chips with my hands. The reason for this is because there may be water in the chip and by me touching it the water may be squeezed out or left on my fingers. I will also make sure that I use the cork borer safely i.e. I will make sure I use it on the table and not my hand.

Variables 

I will vary the concentrations of the sucrose solution; nevertheless, I will keep the volume of the sucrose solutions the same (20cm3). I will also keep the size of the potato chips the same (6cm). I will need to control these factors to ensure that I can obtain the results I plan to obtain. To help me to achieve this I did a preliminary experiment I have based this experiment on the length of the potato chip and the volume of the sucrose solution. This may help me to have results that are correct and precise as possible.

Preliminary Method

1. Collect all apparatus
2. Peel the potatoes.
3. Use the cork borer to make 5 cylinders of potato.
4. Cut the potatoes according to preferable size (no shorter than 5cm).
5. Label 6 test tubes according to what different concentrations you are using.
6. Pour the relevant concentrations into the labelled test tubes.
7. Draw a detailed result table that will make your results easy to conclude from.
8. Put each one of the cylinders in the relevant test tubes.
9. Record the time that you put the cylinders in.
10. Put the stopper (corks) on to stop any of the water evaporating from the solutions.
11.  Leave for 2 hours in a cool place.
12.  Repeat steps 1-10 another 2 more times.
13.  Take results.

Fair Factor

To make this a fair test I will make sure that the same volume of sugar solution is in each test tube. I will also make sure that all the cylinders are put into the solutions at fixed times (preferably a space of 5 minutes in between each trial this way I can make sure that I record the time with precise accuracy). I will also take measurements exactly 2 hours after the experiment was started. This will apply to each trial, which will have a space of 5 minutes in between.

Calculations

I am going to use calculations so that I know the molecular mass of each concentration of the sucrose solution (C12H22O12). To help with my calculations I am going to use the following formula.

Molecular Mass = Atomic Mass x Atomic No.

1 Molar = 1000cm3 + Molecular Mass

Atomic Mass: H = 1

                       C =12

                       O = 16

                               1 Molar = 1 x 22 = 22 + 12 x 12 =144 + O = 16 x 12 = 192

                                             = 22 + 144 +192

                                             = 358 +1000

                                             = 1358

I have used this answer for 1 Molar of sucrose solution to calculate the other concentrations that I will be using. They are masses are as follows.

0.1 = 135.8

0.2 = 271.6

0.3 = 407.4

0.4 = 543.2

0.5 = 679

Preliminary Results

This preliminary experiment will help me to know what kind of results to expect in my next set of results for the other experiment.

I decided to use the mass experiment to put into my original table of results. My reason for this is because I think that the mass experiment will provide reliable and errorless results that I can put into a graph. I have kept the apparatus, variables and safety precautions the same. However, I have varied the method according to the mass experiment, which is slightly different from the preliminary experiment.

Method

1. Collect all apparatus
2. Peel the potatoes.
3. Use the cork borer to make 5 cylinders of potato
4. Cut the potatoes according to preferable size (no shorter than 5cm).
5. Label 6 test tubes according to what different concentrations you are using.
6. Pour the relevant concentrations into the labelled test tubes.
7. Weigh each chip to make sure that they are all the same mass. Make sure not to touch the chip with your hands – if possible weigh the beaker and then weigh the chip inside the beaker, and then subtract the mass of the beaker from the total to get the mass of the chip.
8. Draw a detailed result table that will make your results easy to conclude from.
9. Put each one of the cylinders in the relevant test tubes.
10. Record the time that you put the cylinders in.
11. Put the stopper (corks) on to stop any of the water evaporating from the solutions.
12. Leave for 2 hours in a cool place.
13. Repeat the whole thing 2 more times.
14. Take results.

Results

I have recorded my results to 2 decimal places so that my results are more accurate. However, when I graph my results I will round these decimals to 1 decimal place instead of 2. Consequently I will plot my graph according to the following:

Conclusion

From doing this experiment I have found out that mass is gained when the water concentration of the potato chip is lower than the water concentration of the sucrose solution i.e. the higher the concentration outside the potato cells the less weight. However, when the concentration of the sucrose is too high the water concentration is relevantly higher in the chip. Therefore, the water from the potato chip would have had to osmose into the sucrose solution, which would result in the potato chip.

If you look at the graph you can see a similar pattern of the lines. They all have the shape of a descending curve.

This happened because when the concentration of the sucrose solution was low, the concentration of water molecules on the outside of the potato chips was higher than the concentration of the water inside the potato chip. Therefore, the water outside the cells of the potato eventually diffused into the potato cells, causing it to gain mass and length. However, as I progressively increase the concentration of the sugar solution, the concentration of the water molecules outside the cell of the potato ultimately became less than the concentration of water molecules inside the chip. As a result of this, the water molecules diffused out of the chip and into the solution i.e. the potato chip lost its mass and decreased in length. The potato tissues, being surrounded by a weak solution, were most likely to swell up and become turgid, taking in all the water it possibly could. Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become turgid when they are put in dilute solutions. This occurred when I was performing the experiment in the most identical way. A turgid cell is a cell that is swollen and hard. The pressure inside the potato cell rose and eventually the internal pressure of the cell was high that no more water could enter the cell. When the potato cells were placed in the concentrated sugar solutions they lost their water by osmosis and they become flaccid. The contents of the potato cell shrank and pulled away from the cell wall. When potato cells are placed in a solution that has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. This is shown in the graph. When the concentration was 0.3 the osmotic pressure of the solution and the potato cells where in a state between turgidity and flaccidity i.e. the osmotic pressure between the two were balanced, therefore there was not a change in the mass of the chip or the volume of the sucrose solution.

This scientific knowledge has helped me to explain my conclusion in dignified detail.

My results turned out the way anticipated. I think that both my prediction and my results match quite satisfactorily. Although the two matched, an error occurred in one of my results. I will discuss the matter of this error further in my evaluation.

I think that the experiment worked out quite well. My reason for this is because it was well organised, which made it easy to collect results from and was physically and mentally easier to apprehend. My results showed a clear pattern, which you can see by referring to my graph of results. As you can see, the graph shows a descending curve through the points where I plotted my results. This is the similar pattern that was obtained in my results and this also brings emphasis to the theory of osmosis and my prediction (refer to my plan).

I think that my results were just about accurate enough for the experiment due to the reliability and accuracy of my results. I was able to draw a strong enough conclusion from my results and show a clear pattern from them in which I drew a line of best fit  (refer to my graphs). The different trials I did also showed similar results that proved to have matched with my prediction.

Although my results were reliable enough to draw a strong conclusion there was one error in my results, which I have clearly labelled in my graph. I have thought of the different ways this error could have occurred. They are as follows:

• The potato chip may have been cut too short. To be precise it could have been cut a few millimetres too short.
• The volume of the sucrose solution may not have been measured properly.
• The potato chip may have been dropped into the test tube too hard, which may have caused some of the water to splash out.

I think that my method was probably the best way of carrying out the experiment. If I did it the experiment again I would use a digital stopclock to give me more accuracy for the timing of the experiment. This would enable me to obtain better quality results, in which I could also draw a stronger and more confident conclusion from.

The method gave me results that were reliable and accurate enough for me to rely on to give me sufficient information to draw my conclusion. I also had an amount of results that could give me the information to do so. I was able to count on my results because they were strong enough to give me an adequate quantity of data.

There could be other ways to extend this investigation. I think that it would make the investigation more challenging if I investigated how the diameter of the potato chip is affected by different concentrations of sucrose solution. I could also investigate different solutions and materials other than potato; one of them being water, to see how different solutions with different amounts of water affect different factors of osmosis.

Created by Aaron Miller

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