Plan:
A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1.0 molar. This will be done by adding certain amounts of distilled water to certain amounts of sucrose solution. Potato chips will be cut so they are all the same mass and length. They will be measured using a ruler and electronic scales. This part must be done very accurately as the surface area can affect osmosis. Three chips will be placed in each test tube each time so that I can take an average for each tube. I will use 40 ml of each concentration of sugar solution and once in the test tubes they each will be labelled. The potato pieces will then be placed in the different test tubes and then left over night. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed, re-measured and the final set of results taken.
To do this I will need:
* 6 test tubes.
* 2 potatoes.
* 1 30cm ruler.
* Sucrose.
* Scalpel.
* Scales.
* Distilled water.
* 1 test tube rack.
* Paper towels.
* Cylinder cutter.
Method:
I will take two average sized potatoes and check that they are both healthy. I will then have to get the pieces of potatoes ready. I will push the cylinder cutter through a potato, cutting 18 long cylinders with a length of 50mm. Then I will weigh the 6 sets of 3 potato cylinders. I will have 6 sets because I will have to test the potatoes in 6 different types of solutions; 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose, and distilled water. I will weigh each set and have them ready to put into the test tube, recording all my results as I go. Then i will put the 6 sets of 3 potatoes in the 6 test tubes at the same time and label them. I will leave them overnight. To make the different strengths of solution I will combine 1m solution with distilled water in the following proportions:
Test Tube Number.
Distilled Water.
Molar.
.0
0.0
2
0.8
0.2
3
0.6
0.4
4
0.4
0.6
5
0.2
0.8
6
0.0
.0
After the experiment, I will have to dry the potatoes first, so that the water outside the tissue of the potatoes won't alter the weight of what it is supposed to be. I will quickly take all of them out, and put them onto a paper towel, into their own groups. When obtaining my results, ...
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Test Tube Number.
Distilled Water.
Molar.
.0
0.0
2
0.8
0.2
3
0.6
0.4
4
0.4
0.6
5
0.2
0.8
6
0.0
.0
After the experiment, I will have to dry the potatoes first, so that the water outside the tissue of the potatoes won't alter the weight of what it is supposed to be. I will quickly take all of them out, and put them onto a paper towel, into their own groups. When obtaining my results, I have to reset the balance, so that it would read zero every time I weighed each cylinder. This is to ensure the results are accurate. The reason I use three pieces of potato in each test tube is to ensure I get enough results so that I will be able to take the average of the 6 test tubes. This makes sure that I get accurate results and can overcome any inaccurate results that may have been accidentally made.
Prediction:
Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a holey membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration of the two substances. So in this case, when the water concentration is lower in the potato, the water will go inside it, and the potato will gain weight. If there is very little difference in the two water concentrations, there shouldn't be a big change in weight. And if there is a higher concentration of water in the potato, the water will go out of the potato. The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be water. With this source, the potato will keep on working. When the concentration is lower in the potato, the water will transfer from the solution to the potato. And vice versa.
I predict that the potato in the test tubes with less sucrose in will increase in size and mass. The one in the test tubes with more sucrose in however will decrease in mass. This is because in the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer into the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up, taking in all the water it can possibly take in through osmosis. My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.4 molar solutions of sucrose and greater; this is because the potatoes are taking in the water and increasing in mass, but there is less water in the 0.4 and up solutions so the potatoes will shrivel up and decrease in mass.
Results:
The table below shows:
* The 'Concentration´ column, which are the 6 different types of solutions.
* The 'potato number´ row (1, 2 or 3), which shows the different results for each cylinder in each test tube.
* The weight and length of the cylinders before the experiment.
Before:
Concentration (m)
Mass of Potato (g)
Length (mm)
2
3
2
3
2
3
0.0
0.0
0.0
5.81
5.85
5.87
50
50
50
0.2
0.2
0.2
5.83
5.84
5.85
50
50
50
0.4
0.4
0.4
5.66
5.74
5.87
50
50
50
0.6
0.6
0.6
5.86
5.88
5.87
50
50
50
0.8
0.8
0.8
5.62
5.86
5.81
50
50
50
.0
.0
.0
5.86
5.80
5.64
50
50
50
The next set of tables show:
* The weight and length after the experiment.
* The increase/decrease of the weight and length (calculated by taking the weight or length after, minus the weight or length before)
* The percentage increase/decrease of the weight and length of the potato (calculated by taking the weight or length increase/decrease divided by the original weight or length multiplied by a hundred)
This should help us lead to a more accurate results.
After:
Concentration (m)
Mass (g)
Mass Change (g)
Mass % change
2
3
2
3
2
3
2
3
0.00
0.00
0.00
5.89
5.84
5.88
0.02
0.03
0.03
0.41%
0.62%
0.62%
0.20
0.20
0.20
5.85
5.84
5.84
0.00
0.01
0.00
0%
0.21%
0%
0.40
0.40
0.40
5.69
5.51
5.62
-0.18
-0.15
-0.12
-3.70%
-3.22%
-2.53%
0.60
0.60
0.60
5.63
5.57
5.55
-0.24
-0.29
-0.33
-4.93%
-5.97%
-6.76%
0.80
0.80
0.80
5.49
5.22
5.53
-0.32
-0.40
-0.33
-6.65%
-8.66%
-6.79%
.00
.00
.00
5.23
5.51
5.39
-0.41
-0.35
-0.41
-8.84%
-7.20%
-8.54%
Length (mm)
Length Change (mm)
Length % Change
2
3
2
3
2
3
52
54
53
2
4
3
.04%
2.16%
.59%
50
51
52
0
2
0%
0.51%
.04%
47
49
48
-3
-1
-2
-1.41%
-0.49%
-0.96%
44
46
47
-6
-4
-3
-2.64%
-1.84%
-1.41%
42
45
44
-8
-5
-6
-3.36%
-2.25%
-2.64%
41
42
43
-9
-8
-7
-3.69%
-3.36%
-3.01%
This table below shows:
* The average percentage of mass and length change, which will be used to present the graph.
Averages:
Concentration
Mass % (-/+)
Length % (-/+)
0m
0.55%
.60%
0.2m
0.07%
0.52%
0.4m
-5.89%
-0.95%
0.6m
-5.89%
-1.96%
0.8m
-7.35%
-2.75%
m
-8.18%
-3.35%
On the graphs shown on the next pages, I have made the different solutions as my independent variable, since it won't be changing on any event. And I have made the percentage gain or loss (mass or length) as my dependent variable. I have decided to make it a line graph, because I can then work out the strength of solution and I can tell if there are any improper results. I have taken the average difference of the 6 different solutions and put them on the graph to be more accurate.
Analysis:
In this experiment, I believe that I have collected enough data to support my prediction. This investigation was, I think, successful. Successful meaning my results match my predictions.
The potato cells took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in.
As the masses before the experiment range between 5.62g and 5.87g, this tells us that the potato pieces were cut well, and I believe satisfactory, although they could be improved on. The lengths, however, were all fine. And this tells us that my experiment was successful. The pattern with the % change in the mass table is that the percentages get smaller as the molar solution gets stronger. For the % length change, the same pattern occurs. But the graphs look very different. The mass graph took a big leap at 0.4 M where as the length graph just has a steady slope. This could mean that I had a few odd results but nothing too severe.
I think the difficulties in this experiment were definitely getting the results accurate and working out the averages, the differences and the percentages accurately. But as for the actual experiment, the most difficult part was getting the sizes and masses of the potatoes the same to ensure accurate results. The graph wasn't easy for me to understand at first but I worked it out in the end. Overall my experiment worked well and I am happy with my results.
Laura Hewett
