If the potato is in a high concentration salt solution, the potato mass will decrease because the potato is less concentrated than the salt solution, and the water will move through the partially permeable membrane into the stronger solution.
However, if the potato mass stays the same after the experiment, this means that the water/salt solution and the potato must be of equal concentration.
Equipment
Potato, Borer, Beakers, Measuring Cylinder, Stopclocks, Distilled Water, Electronic Balance, Salt solutions of various concentrations.
Diagram
Method
1) Measure out first solution of 100ml of distilled water and put it in a beaker.
2) Bore the potato.
3) Dry the potato.
4) Weigh the potato using the electronic balance.
5) Place the potato in the first solution, which will be distilled water. Leave it in there for 30 minutes.
6) After 30 minutes, take the potato out, dry it and reweigh it. Record results.
7) Continue experiment by repeating steps 1 – 6, but with 3%, 6% and 9% concentration salt solutions.
8) After doing the experiment using each concentration (O%, 3%, 6%, 9%), repeat three more times, so that you are finished with a set of four results.
Key Factors
The key factor affected in my investigation is the mass of the potato. I am going to change the salt solution concentration used in each experiment. I am going to keep the volume of solution the same (100ml), although the concentrations will be different. I will also keep to using the same type of potato, and the time the potato is immersed in the solution will not differ. The solution’s temperature will be taken before each experiment. It will always be room temperature, but I still need to ensure that my solution’s temperature remains constant.
Measuring
The units of measurement I will use will be grams for the mass of the potato, and I will use an electronic balance to measure it. For measuring volume, I will use a measuring cylinder which specialises in millilitres, and for time I will use seconds and minutes. Time will be measured using a stopclock.
Safety
I will ensure that I don’t drink the solution, and that I don’t accidentally eat the potato. I will also wear protective gloves to ensure that the borer doesn’t accidentally slip and cut me, and I will always point the borer away from me. I will not run in the laboratory, and my total concentration will always be on my experiment, so I can see where a potentially dangerous accident could occur, and I will be able to stop it in time. I will work on an area that has plenty of space and I will ensure that safety is foremost in my mind at all times during this potentially very hazardous time of my Biology course.
Results
Set 1
Set 2
Set 3
Set 4
Average Results
Graphs
(Also see attached graph sheet)
Conclusion
From looking at my results, I conclude that my predictions were correct; when the potato is placed in distilled water the potato mass increases, although not by any large amount. This means that the potato has a stronger salt concentration than the distilled water, as, if the water had a strong salt concentration than the potato the potato mass would decrease and it’s cells would become flaccid. The reason for this is that osmosis is taking place; osmosis is the passage of water molecules from a weaker solution to a stronger solution through a partially permeable membrane. A partially permeable membrane only allows small molecules to pass through, so the larger molecules remain in the solution they originated in.
Evaluation
I feel that I didn’t have any anomalous results, as my graph appears to be in accordance with my prediction. However, I feel that we should have made the original masses of the potatoes the same, as the potato samples used for the 6% solution experiments are nearly a gram lighter than the other potato samples. This was because we were running out of our potato supply, so we should have been more prepared. I would also have liked more results, as you can never have enough results because it is easier to draw up a more definitive and precise conclusion when a lot of results are presented. I could also have tried different types of potato to discover if one type has a saltier concentration than the other. I would also like to a wider range of salt solutions.
