Equipment
- Core Borer ,
- Water,
- Timer,
- Measuring cylinder,
- Potato,
- 0.25, 0.5, 0.75,1 and 1.5 Molar Solutions of Sugar water
- Distilled Water
- Scales,
- Test tubes,
- Test tubes rack,
- Sticky labels,
- Ruler,
- Perpet,
Fair Testing:
In this experiment on osmosis there should only be two changing variables:
1: Different molarities of sugar solution,
2: Change in mass of the potato samples.
To keep these two variables the only variables in the experiment I must:
1: Keep the potato samples the same length. This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will conduct osmosis much more quickly.
2: Use the same potato. This is because many factors due to the potato may affect the experiment. For example the age and sizes might be different, which means one potato might have more water in them then another.
3: Stop the evaporation of any of the molar solution. This is because if the sugar solution evaporates past the level of the potato, then the potato sample will have less surface area in the solution so this would make osmosis happen much slower. To stop any solution evaporating a cork lid can be placed on top of the test tube.
4: Accurate amount of sugar solution: More Bathing solution may affect the rate of solution. To make the amount of solution placed in the test tube as accurate as possible a perpet will be used to measure out the exact amount needed.
5: Contamination: As each test tube is filled up with the different molar solutions the perpet which would measure the amount of solution placed in the test tube may become contaminated with different molarities. To stop his from happening, the beaker and syringe must be washed every time they are used.
6: Average: To make the experiment as accurate as possible an average will be taken out of the 3 sets of results taken. Also any clearly anomalous results will be ignored.
7: Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To keep this from happening, all the test tubes will be kept in the same place and at the same time of experiment.
Prediction
Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain mass. If there is very little difference in the two water concentrations, there shouldn't be such a big change in mass. Also if there is a higher concentration of water in the potato, then the water will go out of the potato and into the liquid solution, as osmosis is the movement of water molecules from a region of high concentration to a region of low concentration, through a partially permeable membrane.
The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working until it dies of either lack of water or too much water, or will stop, as both sides would become equal, making no more reactions. When the concentration gradient is lower in the potato, the water will transfer from the solution into the potato.
In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.
With the potato in 0.1 molar solutions of sucrose, I don't think there will be much change in the weight of the potato. This is because there isn't much difference between the two substances. I believe that the weight and the size of the potato won't be altered much.
The 0.25 molar solutions of sucrose, similar to the 0.5 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction.
The 0.75 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And therefore the weight should decrease, at least for us to notice with the naked eye.
The difference between the water concentration in the potato and the 1 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. As a result, I am sure that the weight of the potato will decrease largely. This is because the potato tissues are surrounded by a stronger solution and it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances. This will also happen with the 1.5 molar solution of sucrose but even more greatly.
My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.25 molar solutions of sucrose and greater.
Method
I plan to carry out this experiment by using all the fair testing procedures to give me the most reliable and most accurate set of results.
I plan to have 5 molarities of sugar solutions prepared with concentrations from 0.1M to 1.5M, this should be more than enough to explain the effects of the potato on osmosis. First sections of potato will be cut using a cork borer and knife to equal lengths (3cm) keeping the surface area constant. I will then weigh each tissue of potato using scales, measured in grams, when I do this I will be resetting the scale every time I put a different section of potato so that I only get the weight of the potato to the nearest decimal. I will then add 20ml of each concentration of sugar in three test tubes, giving me a total of 18 test tubes, and labelling each molar reading. Then to each test tube a cut piece of potato will be added and its concentration added to the label. These will be left for 24 hours. Then the potato pieces will be removed from the test tubes, and surface solution on the potato will be removed using paper towels. I will then measure the potatoes again, recording its change in mass by weighing them. I will then be taking the three readings of each molar concentration. These results will be taken for each concentration in order to get an average and reduce the effect of anomalous resulting.
Results
I compiled a table of results with averages of everything. You can see the table below:
Conclusion
The evidence obtained from this investigation supports the prediction I made. It also shows that the potato cells increase mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration.
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my prediction.
The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue and the concentration of the solution it is surrounded in.
On the whole the my results follow a general pattern, mass decreases as the concentration of the sugar solution increases, there does seem to be quite a few anomalies, for example the 0.75 sugar solution has an average mass decrease of 0.35 while it should fall inbetween -0.2 and -0.24.
This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is the larger increase in grams (mass). This means that the percentage will also be higher, increasing with the grams.
Evaluation
Looking at the overall experiment I have thought of a number of improvements to give me more and better accurate results. Firstly the concentrations were measured using a measuring cylinder and could be made more accurate using titration. Also when the potato was dried to remove surface liquid it was not necessarily done the same on each potato, a more accurate and uniform way of drying would improve the accuracy further.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results; so that we can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tells us how much water could be transferred for each solution.
Also the shape and size could be changed. However this would not affect the results much. This is because the variable would only change the rate of osmosis because of a different weight and size.
Temperature could also be changed for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 3 potato samples could be placed in water baths at 10oC, 20oC, 30oC, 50oC and 60oC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would osmosis the most. This is because at high temperatures the solutions water molecules would move faster and therefore equal the concentration faster.
But overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I'm very please with my results.
