Plan: Variables and Controlled Variables
To keep the test fair, I will need to select my independent variable and my dependent variables and ensure that the controlled variables remain constant throughout the experiment.
The variable I have selected as my independent variable is the concentration of sucrose solution that the potato chips will be placed in. The dependant variables I have chosen to measure are: the mass of potato chip after osmosis and the volume of solution remaining after osmosis. The table below shows all the controlled variables, and how I intend to ensure they are constant:
Plan: Proposed Method
I have considered how I will carry out my experiment, and this is the method I intend to use:
Firstly, I will gather together the different concentrations of sucrose solutions, and use a measuring cylinder to put the same amount of solution into 5 different boiling tubes, placed in a test tube rack, and labelled with their concentration in molars.
Next I will use the potato … and a scalpel to cut the potato into 5 identically sized pieces. I will also weigh each piece and make sure they are of identical mass, it is important this stage is executed accurately since if one piece has a different starting mass or surface area, this could seriously impair the results. I will place one of potato chip into each test tube and begin the stop watch.
After 45 minutes, I will remove each potato chip from the boiling tubes, pausing for a few seconds above the tube, allowing as much of the solution as possible to drip back into the boiling tube, next I will blot each chip with a paper towel to remove the remaining surface water before weighing each chip and recording the results. This also needs to be done as accurately as possible to ensure reliable results.
I intend to repeat each test 5 times, and find an average (ignoring any outliers) to provide as accurate results as possible before creating graphs to display the results and drawing my conclusions.
I will be performing a preliminary experiment to find out how much solution to use, before carrying out the full experiment
Plan: Hypothesis
Osmosis, is the movement of water from a less concentrated to a more concentrated solution through a partially permeable membrane. The less concentrated solution is said to have high water potential, meaning it has more water molecules than the more concentrated solution, the water molecules from this solution will pass through the membrane at a higher rate than the water molecules passing through from the more concentrated solution, with less water potential. This continues, until both sides reach a state of equilibrium, meaning neither side has a higher or lower concentration than the other. I have used this knowledge to try and create a hypothesis.
Using this knowledge, it is my belief that when the potato is placed into pure water, it will have lower water potential, because there are a lot of solute molecules within the potato such as sugar salt etc. Therefore the molecules of water would pass from the pure water through the cell walls and into the cells of the potato. This will cause the cells to swell, and become turgid, as the vacuoles get bigger, the added mass of more water in the cells, should mean that the potato is heavier after the 45 minutes, it should also mean that there is less water left in the boiling tube.
Applying the same logic to an instance where the potato is placed into a highly concentrated sucrose solution, I think the potato would have more water potential. There would be less solute molecules in the potato and so water molecules would pass out of the cell walls into the solution. This will leave the cells flaccid, as the cells lose water and the vacuoles deflate leaving the cells unsupported. With less water the mass of the potato after 45 minutes should decrease, so it would be lighter. I also think that as the water leaving the potato has entered the solution, it should have a greater volume.
As of yet I am unsure what will happen in between the pure water and the extremely concentrated solution. I believe that in some of the really weak solutions the potato will come out heavier as it has more solutes than the solutions. However, at some point the solutions will have more solutes than the potato so it will begin to lose water. I am just unsure as of yet as to where that point will be.
Preliminary: Introduction & Aim
I have chosen to do a preliminary investigation to find out the kind of result I should expect for my final experiment, I will also investigate the length of potato chip I shall use in my final experiment.
The experiment will involve placing different lengths of potato chip into different sucrose solutions with varying concentrations, to find out which one would offer the best results for my full investigation into the effects of osmosis on potato chips placed into different concentrations of sucrose solution.
My aim is as follows:
To find the length of potato most suitable for an experiment to find the effects of osmosis on potato chips placed in different concentrations of sucrose solution.
I hope this preliminary test will make it easier for me to find accurate results in my full investigation and to predict the results I should expect.
Preliminary: Variable & Controlled Variables
Just as with the main investigation to conduct a fair test, I will need to choose the independent variable and dependant variables and ensure the controlled variables remain constant.
For this investigation, I have chosen my independent variable to be the length of potato chip used and the concentration of solution; the dependant variable I will measure is the mass of the potato after osmosis. The table below shows the controlled variables and how I intend to keep them constant:
Preliminary: Method
This is the method I used for my preliminary test:
Apparatus:
- 4 Boiling Tubes
- Test Tube Rack
- Distilled Water
- 1.5M Sucrose Solution
- Potato Borer
- Potato
- Scalpel
- Ceramic Cutting Tile
- Scales
- Measuring Cylinder
- Paper Towel
- Stop Watch
Method:
- Place all three boiling tubes into test tube rack, using the measuring cylinder measure out 20 ml of distilled water and place 20 ml each in two boiling tubes. Also measure 20ml of a 1.5 molar concentration of sucrose solution and place it into two of the test tubes
- Using the potato borer and the scalpel, on the ceramic cutting tile, cut the potato into four chips, the first two 2cm long and the second two 3cm long. Weigh each chip and note down the starting mass, before placing 1 chip in each of the solutions.
3. Time 30 minutes on the stopwatch.
- After 30 minutes, begin to remove the potato, hold each chip above the boiling tube for a few seconds to allow as much surface water as possible to drip back into the tube.
- Blot each potato chip with a paper towel to remove any remaining surface water before weighing the chips on some scales and noting down the results.
- Repeat the tests one more time then use the results to draw graphs and conclusions.
Preliminary: Results
1st Test – Distilled Water
1st Test – 1.5 Molar Sucrose Solution
2nd Test – Distilled Water
2nd Test – 1.5M Sucrose Solution
Averages
The average percentage change for a 2cm chip placed in distilled water is +4.29%.
The average percentage change for a 3cm chip placed in distilled water is +7.83%.
The average percentage change for a 2cm chip placed in 1.5M Sucrose solution is -29.115.
The average percentage change for a 3cm chip placed in 1.5M Sucrose solution is -31.25.
Preliminary: Graphs
Preliminary: Conclusion & Evaluation
Conclusion
The results are very much what I had expected, the potato chips in distilled water, gained mass, whilst the potato chips in a highly concentrated solution, lost mass. This is because the distilled water had higher water potential than the potato, so water passed into the potato during osmosis, whilst the solution had low water potential so the water passed out of the potato during osmosis.
The different lengths of potato, did not change the general outcome, however, it did change the percentage change, percentage changes as you would expect were more significant with larger chips, I think this is because, the larger surface area, gave them more surface for osmotic activity to occur. The smaller pieces of potato, had a smaller surface area, and therefore, less area for the osmotic activity to occur.
In my full experiment, I have decided to use the longer potato chips, since the more varying results will make the test more interesting, and also will make it easier to gauge the results because of the larger changes.
Evaluation
I think the preliminary experiment was both informative and successful. I had no problems throughout the experiment, and I feel confident that the results were both accurate and precise. There were no real outliers, and the results were fitting with my background knowledge of osmosis.
If I did another preliminary in the future, I might be tempted to investigate the amount of solution that produces the best results, or the effect of temperature on the experiment.
Experiment: Equipment
The equipment needed for my experiment will be as follows:
- Several Boiling Tubes
- Test Tube Rack
- Distilled Water
- Sucrose Solutions of varying concentration:
- 0.25M
- 0.5M
- 0.75M
- 1.0M
- 1.25M
- 1.5M
- Potato Borer
- Several Potatoes
- Scalpel
- Ceramic Cutting Tile
- Ruler
- Weighing Scales
- Measuring Cylinder
- Paper Towel
- Stop Watch/Clock/Watch
- Safety Glasses
Experiment: Safety
As with all experiments safety is something that needs to be considered. To do so, I have constructed a table with realistic possible dangers, and precautions I shall use to prevent them:
Experiment: Method
This is the method I followed when conducting my main experiment:
- Gather together all the required apparatus, and make sure you have plenty of space on your workbench.
- Place 7 boiling tubes into a test tube rack, using the measuring cylinder measure out 20ml of each concentration and pour them into each boiling tube. Label the test tubes respectively.
- Using, the potato borer and the scalpel, on the ceramic cutting tile, cut the potato into seven chips, all exactly 3cm long. Weigh each chip and note down the starting mass, before placing 1 chip in each of the solutions.
4. Time 30 minutes on the stopwatch.
- After 30 minutes, begin to remove the potato, hold each chip above the boiling tube for a few seconds to allow as much surface water as possible to drip back into the tube.
- Blot each potato chip with a paper towel to remove any remaining surface water before weighing the chips on some scales and noting down the results.
- Repeat the tests two more times then use the results to draw graphs and conclusions.
Results: Table
These tables show the results I got from my experiment:
Results: Analysis
Results: Graphs
Conclusion: What my experiment shows…
The experiment was almost exactly what I had predicted, it fitted in well with the knowledge I gained through research and I think it was a successful experiment.
In the first two solutions, the potato gained mass, this would suggest to me that there was a higher water concentration outside of the potato, so the water passed into the potato. There was more osmotic activity in the distilled water, because this has the highest water concentration. The effect this had on the potato, was to fill it’s cells up with more water than before, this means that the cells were under higher pressure, which caused the cells to swell and become turgid.
In my opinion the most interesting solution was 0.5M, in this solution, the potato lost just 0.01 grams each time, this would suggest it was very near to the equilibrium. The potato had just a very slightly higher water concentration than the solution itself. Although the potato cells became a tiny bit lower in pressure, the effect was so slight, it was hardly noticeable on examination of the potato, it looked decidedly normal. When the two areas of water are of equal concentration, the areas gain and lose equal amounts of water, so the net water exchange is zero.
As the concentration increased further, the osmotic activity did too, dramatically, at 1.5M the percent change was on average 27.98%. the potato had quite a lot more water potential than the solution, so a lot of the potatoes water passed out of the cells into the solution. This loss of water left the cells under a lot less pressure, the contents of the cells were drawn in, shrivelling up. As this happened, the potato lots its stability and size, it became flaccid.
The experiment, was in my opinion a success, and demonstrated the process of osmosis very well.
Conclusion: Reliability, Precision, Accuracy & Anomalies
Reliability is based on the consistency of a set of measurements, there were very small variations in my results, and for that reason I believe they are quite reliable.
Precision is about how close each different test is in results, there was a little variation here, but never would you expect to see perfectly identical results. Whilst this area isn’t totally perfect, I would say the results are close enough for it to be counted as fairly precise.
Accuracy is to do with how well you read the results, and how carefully the experiment was carried out, I took every care in making sure the results would be as accurate as possible whilst carrying out my experiment, and I am happy that the end results are good, not perfect but good.
Anomalies are deviations from the common pattern, I think there were no real anomalies. Anomalies are often caused by human error, it could be that this one was left on the side longer or maybe the solution was contaminated by a slightly stronger one. However, I do not believe that one anomaly is significant, so long as you have done plenty of retests to expose any outliers so you do not include them in graphs.
Overall I think my data was well collected, in the future, I could pay more care to get even more perfect results, but on the whole, the results I have are pretty good.
Conclusion: Problems
I don’t feel I had any major problems throughout the entire experiment, if I were to pick up on one thing though it would be time management.
Due to the nature of osmosis, the solution needs to be left ideally for at least an hour, seeing as the time the solution was left was a controlled variable, it is crucial it stays constant, I set the time to be one hour, but this meant whilst the results were good, I could not complete an experiment in one lesson.
To overcome this problem, I often set the experiments up prior to the lessons, and took them out during the lesson; this worked well, but was still limited by time-tabling. Staying after school was also problematic due to prior commitments, however, in the end I did manage to get three sets of results, even if it was left a little later than I would have liked.
In the future, I might consider planning more in advance for the experiments, to allow more time to rearrange extra-curricular activities, however, in the end I got the results I needed and whilst the problem was not resolved, it was worked around.
Conclusion: Further Experiments
In the future, I would be interested in investigating further into the equilibrium between the potato and the sucrose solution. Since I already know that the equilibrium must be around 0.5M, I would conduct an experiment to study closer the molar concentrations around this around this area. This would be my proposed method:
- Place 11 boiling tubes into a test tube rack, using the measuring cylinder measure out 20ml of each concentration between 0.4 Moles and 0.5 Moles (0.4M, 0.41M, 0.42M, 0.43M, 0.44M, 0.45M, 0.46M, 0.47M 0.48M, 0.49M, 0.5M) and pour them into each boiling tube. Label the test tubes respectively.
- Using, the potato borer and the scalpel, on the ceramic cutting tile, cut the potato into seven chips, all exactly 3cm long. Weigh each chip and note down the starting mass, before placing 1 chip in each of the solutions.
3. Time 60 minutes on the stopwatch.
- After 60 minutes, begin to remove the potato, hold each chip above the boiling tube for a few seconds to allow as much surface water as possible to drip back into the tube.
- Blot each potato chip with a paper towel to remove any remaining surface water before weighing the chips on some scales and noting down the results.
According to my graph, the equilibrium would probably fall within the range I have planned to test, so therefore, we would find the exact point at which the potato and sucrose solution have exactly the same water concentration.
This extension would hopefully expand my experiment, into a more interesting part of osmosis.