How I will make the data reliable
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed the sugar solution (measured in molars). This will give me a varied set of results from which I hope to make an accurate conclusion. If any of the controlled variables below are not kept constant it would mean it would not be a fair test, in that way giving me false results and an inexact conclusion; for example if the surface area of one chip was greater than the other it would cause the rate of osmosis to change; for there would be a larger rate of osmosis on a larger surface area and vice versa. Also, the measurements for the solutions had to be perfect as to not change the out come of the experiment.
What will I do with the data?
With the data I plan to present it in a graph showing the average percentage change in mass (%) against the molar concentration, showing the osmotic activity between the solution and a potato chip of 2cm.
Safety
Whilst cutting the potato, extreme care and precision had to be taken with the scalpel as it is very sharp and could easily cause a serious wound. I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potato chips
Prediction
My prediction for this investigation the lower the concentration of the sugar solution in the test tube at the beginning of the experiment then the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, to a low concentration i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. In higher concentrations of the sugar solution the result would be that the final mass of the chip would now be smaller than the starting mass of the chip.
Equipment list
- 6 boiling tubes
- 3 potato chips of both 2cm
- electronic lab scales
- 0M-1M of sucrose solution
- scalpel
- clay tile
- measuring cylinder
- stop watch
- beaker
- tissue paper
- ruler
Method
A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar as this should be more than enough to explain the effects of the potato on osmosis. Sections of potato will be cut using a scalpel and will be measured using a ruler at 2cm keeping the surface area constant. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. The mass of each chip will be measured as well, as it is difficult to get the cut potato pieces to the same mass it was decided that I will use a percentage change in mass which will be used to compare the data in the results, as this would be far more accurate. I will do this by taking the difference in mass; divide it by the mass before of the potato and multiplying it by 100. Three chips will be placed in individual test tubes of the same molar so I can take an average for each tube. I will use 10 cm 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 overnight. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed, the reason for this is to lose any excess water which may change the average of my results.
Obtaining Evidence
Analysing and Considering Evidence
What My Graph Shows
On my graph I have decided to plot the average percentage change in mass against the concentration in Molars. I have made the sucrose solution measured in Molars on the x axis and the average percentage change in mass (%) on the y axis. I have decided to make the graph with a line of best fit as it effectively shows the anomalous result and the trend in which Osmosis in a potato chip occurs. The obvious trend in my line graph shows as the concentration of molars increases so that the average change of mass in the potato decreases. At O molars (distilled water) the average change in mass of the potato chip increases by 16.03%. At 0.25Molars of sucrose solution the average change in mass is still positive but not as much; it increased by 10.76, this was anomalous, as the average percentage change in mass of the chip was too high; the result here were above the line of best fit. At 0.5 molars of sucrose solution the change in the average mass decreased as the water molecules went out of the potato due to the sucrose solution having a lower concentration of water compared to the inside of the potato cells; the result here was at -12.15%. By 0.75 Molars, the average change in mass of the potato should have decreased in mass, but it increased compared to the result at0.5M; the average change in mass of the potato chip was at -13.84. So this proved to be my second anomolous reading. By 1M the average change in mass decreased to -27.6.
Why this Has Happened
The resulting graph below shows a curved line, as the chip gets to a point whereby it cannot expel any more water, these cells are called flaccid, plasmolysis occurs in flaccid cells when so much water diffuses out of a cell that there are gaps between the cell membrane and cell wall. At 0M-0.25M the experiment was hypotonic, as the surrounding solution had a higher concentration of water molecules compared to the inside of the cell, so there was a net movement of water molecules into the cell, causing the cell to swell and thus gained mass. At 0.75M-1M the experiment was hypertonic, as the sucrose solution has a lower concentration of water molecules compared to the inside of the cell, and so there is a net movement of water molecules out of the cell; the cells here were turgid.
Does This Agree With My Prediction
The results showed that Osmosis, (the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane); depending on the concentration gradient of the sucrose solution and the water molecules increased or decresed. In this case, when the sucrose concentration is lower than in the potato tissue, the water molecules will go inside the tissue of the potato, and the potato will gain mass, and if there is a higher concentration of sucrose in the potato, the water molecules will go out of the potato. If there is a higher sucrose concentration than in the potato tissue, the water molecules will diffuse from the potato tissue, in this way the potato will lose mass.
This trend I have found does agree with my original prediction, as I stated that due to Osmosis the mass of the potato will decrease as the concentration of the sucrose solution increase. It was obvious that the graph was going to be curved, as eventually the potato tissue will become turgid, and cannot take in any more water molecules.
Scientific Explaination For What Has Happened
Osmosis is defined as the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane.In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution.In a low concentration of water the amount of solute (e.g. sugar) is high. This could be called a strong or concentrated solution.When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium).This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid, at this point the potato increases in both size and mass. If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.The greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water around the cell, the larger the amount of water that leaves the cell. However, there will be a point where the concentrations of water inside and outside the potato cells are equal (isotonic). At this point there will be no change in the length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.
Key
=Water Molecule
Key
=Sucrose molecule
=Water molecule
Evaluating
How Accurate Are My Results
During the experiment I think I have collected enough data to prove my hypothesis that 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 by.
Anomalies and Reasons For Them
We followed the plan successfully, and although I did have two anomalies, I do not think these undermine my predictions that much as the results were not that far from the line of best fit. I believe the pieces of potatoes were mainly cut to the same size with the mass before of most the chips varying, due to some chips being heavieer than others, though all chips had the same surface area. The graphs and results show the very clear fact that Osmosis took place and that as the concentration of sucrose solution increased, the average percentage change in mass of the potato chips decreased. I believe that we had long enough to do the experiment, with one and a half hours to do it in, and the method was quite accurate. On the whole the data fitted in quite nicely with the trend of the trend of the graph. The consistency of the data therefore may be affected by the rush of time to set up the experiment, but I believe I gained consistent and sufficient results, show on the graph and tables. The anomalies occurred at the concentration 0.25M and 0.75M, this may be due to the concentration of sucrose solution not being accurate; this would affect the result as if the concentration was too small or too big, it would cause the mass of the potato chip to increase or decrease more than it should have.The potato chips when recorded after the experiment were not recorded on the same weighing scale, this may cause a slight difference, also when recording the final mass of the potato chip, some potato chips may have been dried more than others.
Improvements To Method
Looking at the whole experiment, I would make a number of changes to improve the quality of the data obtained from this experiment, giving me more accurate results. I would at first try and make the concentrations that were measured in a measuring cylinder more accurate by using a titration; as if a concentration was a little greater then it should have been, it may cause the whole set of results at this concentration to be anomalous. Then, I would make sure, that when each potato chip was dried to remove excess water, it was done fairly, by drying the chips all at once, in this way all of the chips are treated in the same manner. I would further measure the diameter change of the potato, which would help me to find out the volume before and after of the potatoes, as when a chip is turgid it increases in size as well as in mass, and when the chip is flaccid it decreases in size as well as mass. In this way I would be able to find out how far Osmosis has taken place. Using more of the same concentrated Molar solutions, would have helped me to obtain more accurate results, therefore cutting out on the anomalies, this would provide a better line of best fit, as there would be more results, so I would have a better average. I think, we have left the experiment for 24 hours which is long enough for Osmosis to occur, so do not feel that this should be changed. Other extension tasks could be made with different plan tissues like apple. I could also take more results at the molarity levels, for example: 0.2, 0.25, 0.3… etc. The shape and size of the potato could be changed though this would make no difference to a result. This is because the variable would only change the rate of osmosis because of a different weight and size. The temperature may be changed, with varing temperatures instead of just room temperature. The test tubes containing the sucrose solutions and the chips could be placed in different water baths at different temperatures and left for 24 hours. I would expect that at the highest temperature osmosis would be the most. For at higher temperatures the solutions water molecules would diffuse faster and therefore equal the concentration faster. This is because the rate of diffusion is increased by heat to a certain point.
Overall, I think this experiment has been quite a success, and I am pleased with my results.