An Investigation Into the Concentration of Different Solutions

An Investigation Into the Concentration of Different Solutions
Aim: To find out the effect of changing the concentration of different solutions in which potato cores of roughly the same mass are placed. Prediction: I think that the mass of the potatoes will change when they are placed in varied concentrated solutions. I think that if the potato is placed in a strong sugar solution then it will decrease in mass whereas if it is placed in water (a very dilute solution) then the mass of the potato will increase. I believe that this is true because osmosis will occur. Osmosis is the movement of water particles from a high concentrated area to a low concentrated area through a semi permeable membrane until they become evenly mixed. If a potato is placed in a strong sugar solution then the concentration is very high. However this also means that the concentration of water particles is low compared to inside the potato. Osmosis allows water particles to move from the high water concentrated area to the low concentrated area. As water particles are small they can easily pass through the selectively permeable membrane from the higher water concentration to the lower water concentration and the water particles pass out of the potato into the solution. However the larger sugar molecules that are in the solution cannot pass into the potato through the selectively permeable membrane because they are too big. I also think that when the potato is placed in the strong sugar solution that it will shrink. I believe this to be true because by osmosis water is moving out of the potato into the solution. Therefore water is moving out of vacuoles in the potato cells. The vacuole will decrease in size as the water is being drawn out. The cytoplasm will no longer push against the cell wall and this causes the potato to become flaccid. As a result the potato will decrease in size and be quite soft as well as having decreased its mass. If the potato however is placed in a less concentrated solution, such as water I believe that the potato will take the opposite effect. There will be a higher concentration of water particles outside the potato compared to inside the potato and so water will move into the potato as a result of osmosis. Water particles will move through the selectively permeable membrane into the potato cell?s vacuole and cause the cells to become turgid. As water has moved into the potato it will now have a larger mass. As the vacuole size will increase, the cytoplasm will push against the cell wall causing the potato to increase in height as well as feeling firmer. Having taken this all into account I believe that my results will look a bit like this graph: Diagram: Method:
Use a core borer to obtain a large cylinder of potato. Having got
this cut it down into smaller segments of roughly 3 cms using a
scalpel and a measuring strip.
Weigh the potatoes and write down the results.
Pour the volumes of the different concentrated solutions into
labelled boiling tubes and places these tubes in a boiling tube
rack.
With a paper towel, pat the potato pieces so as to remove any
excess water before they go into the different solutions.
Place the potato pieces into the boiling tubes at roughly the same
time.
Allow some time for the potatoes to stay in the tube so that the
results are clear.
To obtain a fair test I will have to keep some factors the same and vary others. Keep the same 1. Temperature ? I will keep this constant by putting all the potatoes in the same room because then all the potatoes will be in exactly the same conditions. I have to do this because I am investigating the concentration of the solution not the temperature, as it too will take an affect on the rate of reaction. 2. Volume of solution ? I will measure all the volumes in a measuring cylinder that will measure to every 0.5cm3. This will make my results more accurate. If I do not use the same measuring cylinder for each solution then it will be harder for me to measure the exact volume that I want. 3. Time ? I am going to try to place all the potatoes into the boiling tubes quickly so that no potato has a significantly larger time than any other to allow osmosis to occur. Then when I take out the potatoes I will remove them in the same order so that the potatoes that went in first will come out last. 4. Mass of the potato ? I am going to cut the potatoes so that they are roughly the same length but more importantly that they are roughly the same weight. This is so that when it comes to obtaining the results it will be clear to achieve an average and to compare the percentage increase or decrease. Things to vary I will be changing the concentration of the different solutions so that I can obtain at least 5 different results to make a good line on the graph. Apparatus:
Potato
Beaker
Measuring cylinder
Scalpel
Boiling tubes
Measuring strip
Electrical balances
Distilled water
Stop watch
Core Borer
Tweezers
Boiling tube racks
Accuracy: To make my results accurate I will be measuring the volumes of the different solutions to the nearest mm³. I will try to make the masses of the potato cylinders as close to each other as possible but if they are very far apart will work out their percentage change relative to their mass. Reliability: It is repeats that make results more reliable so I will be repeating my experiment at least three times and then working out an average from there. Safety: To be safe while I am working I will take care while using the scalpel. I will also clear up any spillages immediately so as to avoid any accidents. I will also be wearing a lab coat. The water, potatoes and sugar solutions are not very dangerous so I will no have to worry too much about this. Preliminary tests: Solution (mols) Volume of solution (cm³) Mass of potato before exp. (g) Mass after 15 mins (g) Mass after 2 hours (g) Difference in mass from start to end (g) 0.0(water)(3) 20 2.05 2.08 2.18 +0.13 0.5 (3) 20 2.26 2.19 1.80 -0.46 1 (3)* 20 2.06 1.98 1.48 -0.42 1 (1)* 20 2.19 2.10 1.58 -0.39
I decided to test whether the potatoes would get a better result if
they were cut into three pieces. This would give the potatoes more
surface area, which would allow more water to travel in or out of
them.
1. I am going to try to get five points on my graph and so I will use different concentrations going up in units of 0.25 mols of sugar solution. (0.0, 0.25, 0.5, 0.75, 1.0) 2. After doing my preliminaries, I decided that I was going to repeat the experiment at least three times to make it more reliable. This would allow me to get an average of the results and would reduce the risk of any anomalies on the graph. So I will set up three test tubes for each set concentration, which gives me 15 boiling tubes to deal with. 3. I am unable to obtain my results after two hours because of a school activity so I am going to have to leave the potatoes in the solution all day. I will collect the results the next morning, which could be anything up to 24 hours. I will record the amount of time using a clock. 4. I have decided to use 20cm³ of each specific solution. This gives a good height of the solution as it covers the potato cylinders. 5. I am also going to cut the potatoes into 3 pieces because this gives potato a larger surface area for osmosis to take place. Also when I compared my preliminary results in which I set up a test to see if I should use one long cylinder of potato or cut it up into three pieces, the cut up potato was the one which gave a better result as there was a larger loss in mass. 6. To make my experiment accurate I am going to have to be very organised. There will 15 boiling tubes on the table at once and so I am going to have be careful that I treat every potato in the same way. 7. When I have obtained my results I will write them up in a table and then record them on a graph. I am going to take an average of the differences in mass and mark any anomalies on the graph. I will know if my prediction is right if the graph that I draw up is similar to the one I sketched in my prediction. Results: Concentration of solution (mols) Volume of Solution (cm³) Mass of potato at start (g) Mass after 19 hours 30 mins (g) Difference in mass from start to end (g) 0.0 20 2.41 2.80 0.39 0.0 20 2.37 2.76 0.39 0.0 20 2.43 2.78 0.35 0.25 20 2.37 2.39 0.02 0.25 20 2.38 2.41 0.03 0.25 20 2.35 2.35 0.00 0.5 20 2.37 1.86 -0.51 0.5 20 2.29 1.82 -0.47 0.5 20 2.34 1.86 -0.48 0.75 20 2.31 1.53 -0.78 0.75 20 2.29 1.57 -0.72 0.75 20 2.39 1.67 -0.72 1.0 20 2.41 1.50 -0.91 1.0 20 2.36 1.50 -0.86 1.0 20 2.22 1.41 -0.81 Concentration of solution (mols) Volume of Solution (cm³) Average difference in mass from start to end (g) 0.0 20 0.38 0.25 20 0.02 0.5 20 -0.49 0.75 20 -0.74 1.0 20 -0.86 Analysis: From the results that I have obtained I can see that if you increase the concentration of the solution then the mass of the potatoes decreases. Also the line that I drew from point to point also shows that it should be a curve and therefore the mass of the potato is not directly proportional to the concentration of the solutions. By looking back at the prediction I wrote before I had completed the experiment I can see that my results fully support what I had said. I had stated that the potatoes that had been placed in a strong sugar solution would feel quite firm whereas the potatoes that had been placed in the dilute solutions would feel softer. Despite not writing this in my results I did test to see whether this had happened and it too was correct. I have come to the conclusion that osmosis has occurred and plays the main part in this experiment. Osmosis is the movement of water particles from a higher concentrated area to a lower concentrated area through a selectively permeable membrane until they become evenly mixed. When the potatoes were placed in the solution of 0.0 mols of the sugar solution there is a higher concentration of water particles outside the potato compared to inside the potato and so water will move into the potato as a result of osmosis. As both the water particles and the gaps in the selectively permeable membrane are small, water can easily pass in and out through the membrane of the potato and therefore osmosis occurs. This means that the mass of the potato should increase as it is now retaining a lot more water. When I check back to see if this information is correct according to my results, the results support my theory. In the solutions which had a higher concentration (e.g. 1.0 mols of the sugar solution) I said that the concentration of water particles inside the potato is much higher than outside the potato. Therefore the water particles inside the potato would move out of the potato through the selectively permeable membrane. The water molecules are small enough to pass through the membrane, however the sugar molecules outside the potato are too big. This means that they will not be able to pass through the membrane and stay in the solution. As a result of this, the potato will decrease in mass as it has lost some of its water particles. Having looked back at my results again I can see that the mass of the potatoes had decreased and therefore I was correct. The results that I obtained have shown to support my prediction very well. I thought that as the concentration increased, the mass of the potatoes would decrease. You can see this very clearly by looking at the graph of the results. It shows a nice smooth curve, which is similar to the one that I drew in my prediction. I repeated each result three times so that I could gain an average result. This was the minimum amount of repeats that I could have done to make sure that they were reliable. I think that I should have maybe done one more repeat for each one result because then it would have me feel a bit more confident that the result were reliable, however this was not really necessary as I feel that the results have backed up my prediction anyway. I also feel that I was fairly accurate with my results. I measure the volumes of solutions very carefully using a measuring cylinder and tried to maintain only a small difference in the mass of the potatoes. I feel that I was accurate enough to show that my results proved my prediction to be correct. Evaluating??. Results Table: In the results table there were a couple of anomalies. In the 0.75 mols solution there was a difference of 0.06g between the results. And also in the 1.0 mols solution there was an even larger difference. The range was 0.10g and the median was 0.86. This could have been for several reasons. When I took out the potatoes and patted them dry I may have absorbed more water out of one of them than from the others. Or I could have not reset the electric scales before placing the next set of potatoes onto the balances. Graph: On the graph one anomaly is clearly visible. This is the potato that was placed in the 0.25 mols sugar solution. It appears to be quite far away from the line that I drew on. I am not sure why this result is so different because when I was doing the experiment I do not remember making any significant mistakes. But there could have been some small mistakes that I made such as not making the concentration of the solution as accurately as the others. Method: I think that the method that used was good enough to give me reliable results. After I had done my preliminary testing, I altered my method so that it would give me more accurate and reliable results. However looking back on the way I did the actual experiment I can think of several things that I could have done better. For example I repeated each result 3 times so I measured out three different solutions of the same concentration. But I think that instead of measuring out 20 cm³ of solution for each result I should have made 60 cm³ of the same solution and then split it between the three boiling tubes. Then the solutions would have been exactly the same concentrations and this would have improved the accuracy significantly as I believe this was my biggest downfall. Conclusion: I am very pleased with my conclusion because it supports my prediction very well. However I think that I should have made more results. The minimum amount of results that you should make to get a good graph is 5 but I think that I should have had 8 or more points on the graph because then I could make my line of best fit more accurate. But this would have been very hard to do because it would mean that I would have had to have at least 24 boiling tubes to deal with! I have already stated that I also wish I had made more repeats of the results with at least 4 solutions for each concentration as this would have improved the reliability too. Proposed extra work to extend the enquiry: Aim: To find out the affect that temperature has on osmosis using potato cylinders and a specific concentration of sugar solution. Prediction: I think that if you increased the temperature then osmosis would be much faster. This is because if the temperature is increased the particles gain heat energy. This gives them more kinetic energy so they would move faster and are more likely to pass through the selectively permeable membrane. Whereas if you decreased the temperature then heat energy is taken away from them and they will move at a much slower rate. Therefore I would expect the graph to look a little bit like this: To make it a fair test you would have to certain things the same: ? The concentration of the solution ? The volume of the solution ? The time ? The mass of the potato

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