References.
Safety.
Safety is important in every experiment. In my experiment I will be using a sharp knife to cut the potato so I will take care when handling that. I will keep the test tubes in a test tube rack in order to make sure they do not smash.
Apparatus.
- Six test tubes
- Test tube rack
- Scalpel
- Pen
- Potato slice
- 5cm³ Syringe
- 1.0M salt solution
- Water
- Weighing balance
- Paper towels
- Stopwatch/ Clock
Diagram.
Variables.
Independent variable: This is the thing I will change in my experiment. I will be changing the concentrations of the salt solutions.
Dependant variable: This is the thing I will have to measure in my experiment. I will have to measure the weight of the potato chips before and after each experiment using a weighing balance.
Control variables: These are the things I will not change. I will be keeping the same amount of solution in each test tube and I will keep using the same potato throughout each experiment.
Fair Test.
In my experiment there should be only one independent variable, which is the salt solution. In order to make sure it is a fair experiment and there is only one independent variable, I must do a number of things.
- Use the same potato in each experiment. This is because the age of more water in it than another and would therefore make the experiment unfair.
- Make sure that the whole surface area of each potato is covered. If some potatoes had different amounts of surface area covered by the salt solution to others, the bits uncovered would not carry out osmosis and so some potatoes would carry out more osmosis than others,which would not be fair.
- Avoid contamination of the concentration of the salt solution by washing and drying each test tube before refilling it.
- Take an average out of the three sets of to make the experiment and results as accurate as possible.
Method.
- First I must prepare the apparatus and take into account the safety procedures and the fair test.
- I must then fill 6 test tubes with salt solution, each one having a different concentration. First the 1.0M, then 0.8M, 0.6M, 0.4M, 0.2M and finally 0M using a syringe. For the 1.0M solution, put in 10cm³ salt and no water. For the 0.8M solution, put in 8cm³ salt and 2cm³ water. For the 0.6M solution, add 6cm³ salt and 4cm³ water. For the 0.4M solution, add 4cm³ salt and 6cm³ water. For the 0.2M solution, add 2cm³ salt and 8cm³ water. Finally for the 0M solution, put in no salt and 10cm³ water.
- Label each test tube as to which molarity solution it contains.
- Cut the potato slice up into long, thin French fries using the scalpel.
- Weigh each French fry and record the weight.
- Place a French fry into each solution.
- Leave for 15 - 20 minutes, timing with a stopwatch or from a normal clock.
- Take out all of the French fries and dry them.
- Weigh each one and record the weight.
- Repeat the experiment exactly.
Results.
Conclusion.
My results show that in a solution of high salt concentration, the potato cells will decrease in weight and in a solution of low salt concentration the potato cells will increase in weight.
I can see that the potato cells carried out osmosis. When placed in a solution of high salt concentration the potato gave out water and decreased in weight. When placed in a solution of low salt concentration the potato took in water and increased in weight.
Looking at my graph, I can see that the percentage change in weight steadily decreases as the molarity increases. I found I had one anomalous result in my first experiment, which seems to be the most unreliable set of results out of the three I took. I can see this because the line for the first experiment does not fit as well as the other two experiments.
From my results and graph, I can see that the prediction I made in my hypothesis was correct. When placed into a solution of high salt concentration, the potatoes did indeed decrease in weight. As I mentioned before, this is because the potatoes have selectively-permeable membranes, and when the concentration gradient is higher in the potato than in the solution, the water will pass through into the solution, and visa versa.
In this experiment, I found that osmosis is the transfer of water from a region of high water concentration through a selectively-permeable membrane to a region of low water concentration and that it does take place within the cells of a potato.
Evaluation.
I think that my experiment was quite fair overall, although I found that my first experiment was not reliable at all. I had one anomalous result within this first experiment, and the other results within it did not decrease in percentage change in weight as the molarity increased as steadily as my other two experiments. The reason for this may be that I did not leave the potatoes in this experiment in the solutions for a sufficient amount of time. After finding these results, I left the other two experiments in for 5 minutes longer than the original experiment, making it so they were left for 20 minutes.
Looking at my overall experiment, there are a number of things I could have done in order to make my results more accurate. Firstly, when measuring out how much salt and how much water went in each solution I used a syringe, but so to make my results more accurate I could have used a burrette or a pipette. Secondly, to get a better average I could have repeated my experiment more times than the original three. Also, I could have left the potatoes in the solutions for a longer period of time to allow osmosis to be carried out to its maximum capability. I could have additionally used more solutions of different molarities instead of only six. To extend my investigation further I could change my independent variable so that instead of changing the molarity of the solutions I could change the type of potato, experiment on different plant tissues e.g. apple, parsnip or change the temperature of the solutions. I could also change my dependant variable so that instead of measuring the difference in weight of the potato, I could measure the difference in length or volume. If I were to change the temperature of the solutions, I would place potatoes weighed beforehand in solutions all of the same molarity and leave them for 30 minutes. When the 30 minutes has been I would take them out and weigh them then record the results. All the same variables would apply apart from the independent variable which would be changing the temperature rather than the molarity of the solutions. I predict that I would find in this experiment that osmosis would take place the most at a higher temperature. I think think this because at higher temperatures the solution’s molecules would move faster and so reach the state of equilibrium faster.
Overall, I feel that my results were quite accurate and fair and this is due to the precautions I took to make this a fair experiment. However, I believe there are still certain aspects that could have been made more reliable and had I had more time, I would have carried out these additional experiments and precautions.
