Cell Wall
Cell Membrane
Vacuole
Nucleus
Low Water Potential
I am aiming to find the salt water concentration that causes the potato chips to neither swell nor shrink. This solution would therefore have to contain the same concentration of free water particles outside the chip than there would be inside the cells, so that equilibrium would be achieved, allowing the water to enter and leave the cells at the same rate, by osmosis. This would therefore cause the chip to neither swell nor shrink.
Variables:
Independent: The range of concentrations will be from a 0% to a 10% salt water concentration, increasing in two’s: 0, 2, 4, 6, 8, 10%.
Dependent: I am going to find the potato chips mass before they are immersed, and their mass after twenty-four hours in their own solution. I will then find the change in mass and compare the change in mass to the percentage change in mass.
Control: Same size cork borer, same total volume of solutions, same size test tubes, same top-pan balance, same potato type, same size syringes, same size potato chips, same blotting time, same weighing time, same cutting time and the same immersion time.
Replicates:
I will repeat each concentration three times and obtain an average percentage change in mass of the potatoes in their concentrations.
Plan:
- Collect a 10% salt solution in a beaker, and a volume of distilled water in another beaker.
- Obtain 18 test tubes and enough test tube racks to hold all of the test tubes.
- To create the less concentrated solutions, the 10% salt solution will have to be diluted with the distilled water. This can be done by executing the following dilutions:
- You will need to use separate syringes to transfer each liquid into the test tubes, to ensure accurate concentrations.
- Each concentration should be replicated at least three times.
- Label the test tubes with their concentrations.
- Next, using a cork borer bore enough cylinders from the potato to obtain 18, 3cm potato chips.
- From this point, you must work quickly because once the cylinders have been cut; they will be losing water vapour by evaporation, which will affect the experiment. The potatoes would have lost mass due to the loss of water vapour; so therefore, there will be less change in the mass of the chips.
- Next, using a scalpel and ruler, cut 18 potato chips from the bored cylinders. They must have a length of 3cm and a diameter of 6mm.
- Osmosis is slow and as the experiment is going to be completed over twenty-four hours, you will need to make the process of osmosis as quick as possible. By using a cylindrical shape, there will be a greater surface area in proportion to the chips volume, so osmosis will occur at a faster rate, as there will be a larger space for the water to enter or leave the chip. Also, this shape duplicates that of a chip, so the experiment would be more equivalent to the problem that the chip shop owner has.
- Next, blot each cylinder, making sure that each chip receives the same blotting time, so that the experiment is fair and accurate, as some chips may have had a longer blotting time, which would result in more water vapour loss by evaporation, than the others. This would affect the experiment because if a chip has lost a lot of water, then it would have lost mass, so consequently, there will be less change in mass.
- Weigh each chip using a top-pan balance. Ensure that you use the same top-pan balance to obtain ultimate accuracy when possible. Also, make certain that each chip is weighed for the same length of time, so that it is fair and each chip loses the least volume of water vapour that could be evaporated potentially at this point.
- After all of the chips have been weighed, place them into the solutions in the test tubes, preferably all at the same time, to make it a fair test.
- Once all of the chips are in, cover each test tube using cling film and sellotape. This will prevent loss of water vapour by evaporation, which would cause an inaccurate experiment. The experiment would be inaccurate if the test tubes were not covered because this loss of water would lower the concentration of free water particles outside of the chip, which would then cause there to be a possible higher concentration of free water particles inside the chip, so water would move out by osmosis, when it should have moved in. The potatoes in these solutions would become flaccid and lose mass.
- Shake each test tube so that the solutions are well mixed and all of the particles are able to surround the chip equally.
- Once the test tubes have been shaken, start the stopwatch.
- Allow the chips to remain in the solutions for twenty-four hours, as osmosis is slow because it does not require energy.
- Replications of the concentrations will enable you to identify any anomalous results, and to then discard them. They also allow you to calculate a mean result, which is more reliable than one result.
- Record your results in a results table and produce a graph that shows the percentage change in mass against the concentrations.
Apparatus:
Cork borer: 6mm diameter
18 Test tubes
Blotting paper
Top-pan balance
Test tube racks
Ruler
Scalpel
Stopwatch
Two syringes
Potato
Fireproof mat
Cling film
Sellotape
Forceps
10% salt solution
Distilled water
Two beakers
Safety:
Care should be taken when cutting the potato cylinders with a scalpel.
Method:
We executed the experiment exactly as we planned it. However, there were some few minor changes. For example, we used forceps to transfer the potato chips and a fireproof mat to cut the cylinders on.
Results:
() = anomalous result
Mass of potato chips before immersion:
Mass change of potato chips after twenty-four hours:
Average change in mass
Percentage change in mass=Average potato chip mass X 100
Percentage change in mass:
Graph Analysis:
From the graph, I can estimate that the most suitable concentration is between the 4% and 6% salt water concentrations. Therefore, I can estimate that a 5% salt water concentration is probably the correct concentration that causes the chips to neither swell nor shrink. The 0% salt water concentration caused the highest percentage change in mass because it was just distilled water which meant that there were more free water particles on the outside of the potato chip than there were inside, so the water entered the chip by osmosis, from a high concentration of free water particles, to a lower one, causing the cells to become turgid and consequently gain mass. From the 6% salt water concentration upwards; the potato chips have lost mass. This is because there would have been fewer free water particles outside of the chip than there would have been inside, so water would have left the chip cells by osmosis, from an area of high water potential to an area of low water potential, causing the cells to become flaccid and therefore lose mass.
Conclusion:
I found that a suitable salt water concentration is between the 4% and the 6% concentrations. This is because the 4% conclusion caused the potato chips to swell the least, and the 6% concentration caused the potato chips to shrink the least. Therefore, I can predict that the more accurate concentration must be about 5%.
Explanation of Conclusion:
The 4% concentration must have been too weak, as there must have been a higher concentration of free water particles outside the chip than inside, so the water entered the chip by osmosis, from an area of high water potential to an area of low water potential, across the partially permeable membrane, causing the cells to become turgid and therefore gain mass.
The 6% concentration would have been to concentrated, because there was a lower concentration of free water particles outside the chip then inside, so water left the cells by osmosis, instigating them to become flaccid and therefore lose mass.
I can estimate the correct concentration to be around 5%, because from looking at the graph, you can see that there is no percentage change in mass for the 5% salt water concentration. I can therefore predict that at this concentration, water is entering and leaving the chip cells by osmosis, at a constant rate, from an area of high water potential to an area of low water potential, across a partially permeable membrane. This means that equilibrium has been achieved, which causes the chips to neither swell nor shrink.
The other concentrations must have been either too weak or too strong, as the rest of these salt water concentrations caused a percentage change in mass, but if they had been a suitable concentration, then they would not have caused any change in mass.
Evaluation:
My results were fairly accurate, although there appears to be one slight anomalous result, for the 10% salt water concentration. This could have occurred if the chips for this concentration received different lengths of time for blotting, cutting, weighing and immersion in their solutions. If these chips gained more of these times, then they would have lost more water vapour by evaporation, which would consequently cause less change in mass. My results are reliable because I replicated each concentration three times and I was therefore able to identify any anomalous results and discard them, and also calculate a mean result, which is more reliable than just one result. To improve the experiment, I could improve the overall accuracy of how it was executed. For instance, I could ensure that any preparations are completed for the same lengths of time, for example, the cutting and weighing times. To improve reliability, I could replicate five times instead of three, which would mean that I could discard any anomalous results and calculate a more reliable mean result, which is better than just one result. For further work which would provide additional evidence to support my conclusion, I could investigate more accurate concentrations, such as 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8 and 6% salt water concentrations, as I know that the most suitable concentration is around 5%. To extend my enquiry, I could investigate other variables that might affect the rate of osmosis, and therefore, the change in mass of the potato chips. For example, the surface area of the chips might have an affect, because the larger the surface area of the chip in proportion to its volume, the faster the rate of osmosis, as there would be a greater region for the water to enter or leave the potato chip cells, at a much faster rate. Also, we could investigate how the temperature affects the rate of osmosis. Perhaps if it is warmer, then osmosis will occur at a faster rate because the enzymes will have energy to move quickly.
