Safety:
- Wear safety goggles at all times
- Use the knife very carefully as it may be hazardous to yourself or people around you
Minimize the risks by working independently and in your own space, do not get too crowded.
Method:
- Cut a potato into 12 equally sized chips without any skin
- Accurately measure the weights of all 12 chips and mark them so that you know which one is which.
- Measure out 50cl of each of the following concentrations of the salt solution using salt solution and distilled water.
0.1M
0.2M
0.3M
0.4M
4. Place 3 potato chips into each of the 4 salt solutions and leave them for 52 hours.
5. Take out the potato chips and gently dry them with a paper towel
6. Remeasure the mass of each potato chip and work out the difference in mass from before and after the chips had been left in the salt solution.
7. Work out the percentage mass change of the chips for each of the different salt solutions and this will show how much osmosis is taken place.
To work out the percentage mass change uses this formula:
(Mass Change x 100) = Percentage mass change
Start mass
Fair Test:
I am going to make this a fair test by making sure that all of my potato chips are almost exactly the same size, all without any skin on them and all with around the same surface area. This is because the skin and surface area could affect how much osmosis takes place.
I must use the same amount of salt solution for each concentration, I am going to use 50cl of salt solution for each concentration.
Osmosis
- Water particle
- Direction of water movement
This Experiment
LOW CONCENTRATION HIGH CONCENTRATION
SALT SOLUTION SALT SOLUTION
-Salt Particle - Potato chip
-Water Particle - Direction of water movement
As you can see, in the low concentration solution the osmosis is going from outside of the potato chip to inside. Whereas is the high concentration salt solution the osmosis is going from inside of the potato to outside.
When the osmosis goes from outside the potato to inside it the potato cells fill with water and become turgid. When the water goes from inside of the potato to outside the potato cells loose the water inside them and become flaccid.
Prediction:
I predict that the chips in the 0.1M salt solution will gain the most mass because when I did my preliminary experiment using salt solutions of 0.0M and 0.5M I found that the average percentage mass change in the 0.0M solution was 22.46%, but in the 0.5M solution it was -29.64%, this shows that the chips in the 0.5M solution actually lost mass; this was because there was a higher concentration of water inside the potato chips than in a 0.5M salt solution and therefore the net movement of water was from inside the potato to outside.
The reason I am using the 4 concentrations of salt solution that I am is because they are all between 0.0M and 0.5M, and in my preliminary work I found that 0.0M was too low a concentration because the chips gained mass, and 0.5M was too high a concentration because the chips gained mass.
Results:
These are the results that I got from my experiment:
The results show that as the concentration of salt solution increases the average percentage mass change decreases, this means that the higher the salt solution concentration the less osmosis that is taking place from outside the potato cells to inside the potato cells.
However, once the salt solution concentration reaches a certain point the osmosis starts to take place from inside the potato cells to outside ,this means that the potato chips looses mass.
I am going to use graphs to try and show the exact point where the mass change changes from being a positive change to a negative change, this will then show me the salt content of the chip.
Sketch Graphs:
I am expecting for my graphs to looks something like these:
Graphs:
Average Percentage Mass Change:
(hand drawn)
This graph shows an approximate amount for the measurement of salt in a potato chip, it is only approximate because it uses the average measurements and also has a line of best fit.
The point where the line of best fit crosses the X axis is the approximate measurement for the amount of salt in a potato chip.
This measurement is 0.15M.
Percentage Mass Change:
(hand drawn)
This graph shows each of the separate results from the potato chips at different concentration salt solutions, it also shows the averages.
The line is curved and is therefore more accurate than the
line of best fit.
The point that the line crosses the X axis is 1.25M.
Conclusion from my Graphs:
Both of my graphs do look how I predicted they would when I drew my sketch graphs.
I think that the Percentage Mass Change graph is slightly more reliable than the Average Percentage Mass Change graph because the Average Percentage Mass Change graph uses a line of best fit, which is not as reliable as the curved line which I used on the Percentage Mass Change graph.
Conclusion:
Overall I think that this experiment worked well. However I think that I could improve it next time by
- Running each of the concentrations of salt solution 5 times instead of 3 so that I would get a more reliable average result from each of the concentrations of salt solution.
- Using another 4 concentrations of salt solution-
0.15M
0.25M
0.35M
0.45M
I would do this because it would mean that I would get a more accurate final result from the experiment.
- I would create a graph showing the Mass Change as well as the two graphs that I made during this experiment showing the Percentage Mass change and the Average Percentage Mass change. I would do this because it would show me the actual Mass’ that the potato chips gained and lost during the experiment as well having the other graphs showing me the percentage mass changes.
I found that the concentration of solutes in the cytoplasm of plant cells, or in other words the amount of salt there is in a piece of potato was approximately between 0.125M and 0.15M.
I found this out because between these two concentrations of salt solution the potato chips neither gained nor lost a measurable amount of mass.