I have predicted this as water moves from a place with higher water potential to a place with low water potential, through a partially permeable membrane. The more water the potato chip absorbs, the higher the mass should be. Thus
The cell walls in the potatoes are partially permeable so I am expecting for osmosis to take place in them.
My mass loss/gain graph prediction:
Initially, the concentration and the water loss/gain would be directly proportional, but as the water potential is decreased, the graph line would start to level off because there would not be enough water in the chip, as the cells would be flaccid.
Apparatus
Uncooked Potato chips (5cm)
10cm³ syringe
Test tubes (10)
Test tube holders (2)
Saturated salt solution
Distilled water
Blotting paper
Kitchen towels
Stop clock
Scalpel
Forceps
Cork borer
Method
Potato chips were made from cutting it with the cork borer. They were cut to 5cm in length, using the scalpel and weighed to make sure it was a fair experiment, and that they were the same size. In this experiment, I am only going to change the concentration of the solution, so making sure that the chips were the same size was important in ensuring the experiment was fair. Ten test tubes were filled with different concentrations of solution. (See table above), the additional five were repeats, to make sure I got the most accurate results possible. To do this, I used the syringe, as I felt it would be far more accurate than a measuring cylinder. Each of the test tubes was labelled according to their contents. One potato chip was placed into its solution every minute, and make sure that they would all stay soaked in it for exactly the same time to ensure it was as fair as possible. I left the potatoes in for 50minutes each. After being taken out their solution, they were each re-weighed and results were noted.
Before and after the experiments I will measure and weigh the chips, measuring will be recorded the nearest 0.1cm. Weighing will be recorded to the nearest 0.01g. I have tested solutions up to 40% of salt as I cannot test for any more concentrated, as at 40%, the solution becomes saturated, meaning it is the most salt that can be dissolved into water.
I have done repeats for every single solution to try to get more accurate results.
I used the same potato so all my potato chips should be equal in water potential before blotting.
I did the experiments at the same time on the same day so the room temperature should be the same for each potato.
Safety precautions:
- No running in laboratory.
- Scalpels not to be placed around, and used with care.
- Hair tied back.
The Preliminary experiments
In this experiment, I did almost exactly as above, in the method. Apart from two major differences:
- Chips left in for only 10 minutes
- Chips were put in at same time
The problems I found from this were that 10 minutes are not enough time for a great reaction. This helped me decide to leave them in for 50 minutes; this was almost the longest time I was able to leave them in for. Also that the chips could not be placed in their test tubes at exactly the same time, this made the timing unfair, so I then decided to put one chip in its test tube once a minute, and count to make sure they were all in the solution for the same time to make sure it was a fair experiment.
Results table to show mass and size of potato chips change depending on the concentration of the salt in the external solution
Results in orange are my repeats
How I calculated the percentage of loss or gain in mass.
Mass of chip after X 100
Mass of chip before
Answer was then taken away from 100 to work out the loss/gain.
Example:
1.86 X 100
2.35
= 79 (2.sf)
100-79 = 21%
How I calculated the average loss or gain of mass in chip.
Loss/gain of mass in original experiment + loss/gain of mass in repeat = average
2
Example how I found the average gain of mass on the 0% experiment
(6+5) = 5.5%
2
Analysis
The graph shows that osmosis has occurred. My results have not agreed with my prediction. I predicted that the more concentrated the solution is, the more water the potato would lose by osmosis, as osmosis is when water molecules move from a high concentration to a low concentration. From my graph, I can say that my anomalous results were those done for 30% and 40% salt concentration. This disagrees with my prediction graph, as I predicted the graph to go in a straight diagonal line to show that it is directly proportional. My graph curves, this could be because they I have anomalous results.
The 0% salt solution results came out exactly as planned, the results are reliable as the two points both for the experiment, and the repeat are fairly close, and the average is right between them.
Between the 0% and the 10% solution, the mass of the potato chip dropped dramatically, I am suspecting my result for this experiment is quite accurate though, because both my original and repeat experiment results came out very similar. This is shown on the graph by the two points of which are the results. They are quite close together.
The 20% experiment went fairly well also. The potato mass still decreases as the concentration of the solution rises. Though my first experiment for this did not drop, it in fact it starts to rise again. The repeat and the average for this experiment dropped in mass, so it must mean that the original one I did must be anomalous.
It is at 30% when my results begin to disagree with my prediction. The graph begins to curve upwards. They are most probably anomalous results, as according to my background knowledge, this should be not happening. The two points on my graph of original and repeat experiments are quite far apart, but they both disagree with my prediction.
At 40%, the line of average rises even more in my graph, the points are fairly close together, but it is very likely they are both anomalous. All the anomalous results are circled in my graph.
From the first three experiments, I noticed that there was a trend between the concentration and the loss of mass. The graph shows that the higher the concentration got, the more mass the chip would lose. This part proves my hypothesis correct, as water moves from a high water potential to a low water potential.
I expected the graph to have a straight diagonal line down until it eventually curves to a flat line when no more water can diffuse from the potato chip into the salt solution.
In conclusion, I have proved that my prediction was correct. However, some of the conditions in which I did my experiments may have caused the latter of my results to agree with my prediction.
I also noticed that the chips that had been placed in a very concentrated salt solution had decreased in length. This means that water has moved out of the cells and they are turgid. Chips that were placed in distilled water however had increased in size. Meaning water had moved into their cells, making them turgid.
Evaluation
Overall, the experiments went quite well. There weren’t any faults with the actual experiment, as I had done preliminary experiments that helped me decide what would be the most appropriate way of carrying out my experiment.
Most of the results were fairly reliable, but a few of them did not turn out as I had expected them to.
There are several reasons as to why I had a few anomalous results; firstly, I used a different balance to weigh the potato chips after the experiment. The potato chips may have been accidentally mixed up, during the weighing processes. It is possible that I blotted some of the chips more than others. This would make a difference to the masses of the potato chips.
I feel that the evidence is not totally reliable to support a firm conclusion about my hypothesis on osmosis. Further work will have to be carried out in order to create firmer and more dependable evidence.
Another way of improving the results would have been to leave the potato chips in their solutions for a longer period of time, this would have enabled me to find the saturation point (when the potato can no longer take in any more water) and dehydration point (when the potato cannot lose any more water) and I can therefore get a more accurate result.
To carry this investigation further, I could do repeats of the experiments with anomalous results. But they cannot be totally reliable because I would have to use a different potato, balance, and the room temperature may differ. I could have also did experiments for a 2%,4%,6% and 8% salt concentrate to investigate whether on my graph, the results would be drawn out in a straight line, or a curve.
I could also use a more accurate balance, which weighs to a smaller number of decimals. The balance I used for these experiments weighed to the nearest 2 decimal points; maybe I would have had more accurate results with a balance that weight to the nearest 4 decimal points.
I could have also extended the experiment to a more exact level by looking at the potato chips under a microscope, and then I would have then been able to see the cells in greater detail and draw some more observational results.
