Method
- I will make up six different solutions; one of 0% salt concentration, one of 2% concentration and so on, up to a 10% salt concentrated solution. In order to gain accurate percentage measurements when making up the solutions I will use 100ml of distilled water with (for example) 4g of salt (this would be for a 4% concentrated solution).
0%=100cm3 water+0g salt
2%=100cm3 water+2g salt
4%=100cm3 water+4g salt
6%=100cm3 water+6g salt
8%=100cm3 water+8g salt
10%=100cm3 water+10g salt
- Then I will decant 35cm³ of each solution into six boiling tubes. This measurement of water allows enough volume of solution for the chip to be emerged but so that the boiling tuber will not overflow. I will put cling-film over each boiling tube to prevent evaporation of the solution.
- I will cut the potato chips using a cork borer. Each chip will be as long as the potato allows but all chips of equal length. They must also have square ends to ensure length-measurements are accurate.
- Before putting the potato into the solution I will measure the length of the potato chips and record it.
- I will put one potato chip in each solution and leave it to react for as long as convenient. This will probably be 1 hour.
- After the potato chips have been soaked in the solutions for one hour, I will remove each chip using tweezers and then measure and record the length of each chip. I will measure in mm, with an accurate ruler for fair, detailed and accurate results.
- I will use the remaining potato to cut six more chips and place them in six boiling tubes, all containing the same six solutions as the first set of potato chips. I will carry out the experiment for the second set of chips in exactly the same way as I did for the first set. This will allow me to take an average of the two sets to gain more accurate results.
Apparatus
The apparatus that I will use in this experiment is:
- Salt
- Beaker X 12
- Distilled Water
- Boiling tubes X 12
- 1 large baking potato
- Cork borer
- Knife
- Accurate ruler
- Accurate scales
- Measuring tube
- Tweezers
- Cling film
Safety
I will conduct this experiment safely by:
- Being careful while handling knives and similarly sharp objects.
- Moving carefully around the lab to avoid accidents/collisions.
- Handling all glassware with care to avoid breakage and injury.
Prediction
For the potato chip left in water (0% salt concentrated solution), I predict that water will move by osmosis, from the high concentration of water (in this case, the solution) To a low concentration of water (the potato cells). The water will transfer into the vacuole and cell sap of the potato cells, this will exert pressure on the cell walls and the potato cells will become turgid.
Because each potato cell becomes turgid, the potato chip will extend in length. Because of the cell-expansion, the potato chip will become stiff.
The potato chip in the solution of 10% salt concentration will decrease in length. This is because the high amount of salt in the solution means that there is more water in the potato cells than in the solution. This will result in water molecules travelling by osmosis from the high water concentration in the potato cells, to the lower water concentration in the salt solution. The cells plasmolyse, this will cause the chip to become flaccid, or floppy.
The chips in the solutions with salt concentrations of 2-8% will get progressively smaller. The general pattern will be ‘the higher the salt concentration, the smaller the chip becomes’-because it looses more water to the solution through osmosis. One of the chips will remain the same length because there is the same concentration of water in the potato cell as in the solution.
I will expect my result graph to look like this:
At one salt concentration there must be equilibrium between the concentration of water in the potato cell and in the salt solution. This will mean that no osmosis takes place. Using a graph like the one above, we will be able to see where the equilibrium is, and at what salt solution it occurs, and therefore, the salt concentration within the potato cell.
Results
Because I took two sets of results, (from one potato) in order to increase the accuracy of my results, I have noted the results from both sets below, but have used the average to draw a conclusion for the experiment.
Conclusion
From my results, it is clear to see that my prediction was correct: “as the concentration of the salt solution increases, the length of the potato chip decreases”.
0% and 2% salt concentration
In these cases, because there was no or very little salt, there was more water outside the potato chip than inside the potato cells. This meant that water travelled by osmosis, from the water, into the potato cells, causing the cells to expand and the potato chip to become turgid, or stiff. Because the potato cells expanded, the length of the chip increased. The potato in 0% salt concentration increased in length by 2mm, the potato in 2% concentration solution, lengthened by 1mm.
4% salt concentration
There was no change in the length of the potato chips in this salt solution. This must be because there was an equal concentration of water in the solution as there was in the potato cells, therefore, no osmosis took place and the cells were not changed in any way to affect the potato’s length.
6, 8 and 10% salt concentrated solution
These solutions had similar effects on the potato chips. Because there was a small concentration of water in the solution, the concentration of water in the potato cells was greater. This meant that water travelled by osmosis, from the potato cells, into the solution: which caused the potato cells to plasmolyse and the length of the potato chip then decreased. The potato chip became flaccid, or floppy. The length of the potato chip in the 6% solution decreased by 1.5mm, the length of the potato chip in the 8% solution decreased by 2.5mm, the length of the potato chip in the 10% solution decreased by 3.5mm.
Evaluation
Although the results I gained from the experiment were as expected and correspond correctly with my scientific knowledge, the accuracy of the experiment could have been improved. I could have done this by:
- Repeating the experiment more than twice.
- Using a wider range of salt concentration solutions (for example, instead of using 0-10% at 2% intervals, I could have done it at 0.5% intervals: 0%, 0.5%, 1%, 1.5% etc)
Despite being unable to do this, I think that my results are both accurate and reliable.
