Above are the variables which can effect osmosis and would lead to different results but to enable a fair test I am going to only change the variable which was listed in the non variable section; concentration of volume.
Prediction:
My prediction is that when the potato chips are put into the increasing molar solution they will decrease in weight. Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. The potato chip has a permeable membrane with small holes in. the holes are so small that only water molecules can pass through and bigger molecules like sucrose cannot. An example of a partial permeable membrane in industry is the kidney dialysis machine. The water molecules pass both ways through the membrane but because there are more molecules on one side than the other there is a steady net flow into the region of the low concentration which is the stronger solution, in our case the sucrose solution. This causes the sucrose concentration to fill up with water and the water tries to dilute it. This will lead to a state of equilibrium and this will be shown as the iso osmotic point.
Range of possible solutions which will be used for the experiments:
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 m sucrose solution. After depending on how the results vary across a graph I will then go to more of a precise molar solution i.e. 0.15m etc
There are many reasons why I have chosen the range. Firstly if we look at the second set of results which I will possibly use is because it will be a wide range which will lead to more accurate results. Another reason why it is to have a wide range is that if you only have for example 1m – 1.5m solution you will only be seeing the effect of osmotic activity in a higher concentration and not a lower concentration which would mean I would only be taking results from a higher concentration not the lower. This would mean that the investigation will be unfair. Another reason why I chose the wide range is because if I have a large range then it will be easier to pin point the iso-osmotic movement where there is equilibrium of water on both sides i.e. in the potato cell and the sucrose solution. Accuracy will be conducted during the investigation because if I do anything inaccurate then the results will be inaccurate. Also the investigation will be a failure and then a fair test will also be criticised. I shall try to duplicate each experiment for many reasons. Firstly because if you repeat an experiment you have more reliable results and also repeating an experiment you get rid of any anomalies created in the last experiment such as an error on measuring the chip or anything similar.
Osmosis also takes place in plants and it contributes to a very important factor which will be discussed further. Osmosis takes place between the cytoplasm and the solution outside the cell. The changes happening inside the cell due to osmosis bring about visible changes in the plant. However when the plant cell is placed in less concentrated solution water passes through the cellulose cell wall and the cytoplasm and eventually into the vacuole leading to the cell becoming turgid. This happens when water flows through the cell wall and into the vacuole. The pressure of the water in the vacuole increases and the water presses the cytoplasm against the cell wall. When the cell contains as much water as it can the cell is fully turgid. However when plant cells are put in higher concentrated solution water passes out of the vacuole, out of the cytoplasm and into the surrounding solution. The pressure of the vacuole on the cytoplasm decreases and the cytoplasm pulls away from the cell wall. The cell becomes limp something like a balloon and the cell is called plasmolysed or flaccid.
Obtaining
To start this experiment we needed the necessary equipment. The equipment consisted of a 25 cm3 measuring cylinder, a knife to cut the potato chips, two tiles, and 6 boiling test tubes in a test tube rack, a solution of 1 molar sucrose (sugar) solution, distilled water, a pipette, and then the potato chips. My partner and I wanted to see two sets of results i.e. a duplicate. This would lead to more precise results and because we were doing duplicates we needed a further 6 boiling tubes. First of all we started to make the solutions in the test tubes according to the molar variables that we had selected. Our variables consisted of 0 molar sucrose solution (pure water), 0.2 molar sucrose solution, 0.4 molar sucrose solution, 0.6 molar sucrose solution, 0.8 molar sucrose solution and 1.0 molar sucrose solution (pure sucrose solution). To make these solutions we followed a simple protocol. For example to make a 0.2 molar solution of sucrose in a total volume of 30 cm3 we had to get 6 cm3 of sucrose solution (2×3) and 24 cm3 of water which would equal 30 cm3. As we had 12 test tubes in total i.e. 6 were the duplicates the same variables were also used. We then started to cut the potato chips. Here we had to be careful because we were using knives to cut the end of the potato chips, if the potato chips had any skin on or to cut to length. Obviously we needed to cut of the excess skin because then water will be restricted to get out of the water which could lead to wrong results. We needed the potato chips equal in length because if they were not then it would not be a fair test and also we would be going against a variable that we were not meant to alter in the first place. We then dried the potato because that could lead to excess weight and then measured the potato chips. They all measured 3.2 cm and we measured from one end to the other. Below the diagram showed how we did that.
This is the length we measured. Here the question could arise, what about the circular sides of the potato chips? For this we had two tiles where we would place the potato chip and this would lead to the chip, if being uneven the chip would fall and if equal it would stand up. After measuring them and then noting the weight and length of each chip we then put them in each of the solutions. Also we labelled the test tubes with our names. This helped by identifying the test tube instantly and didn’t cause no confusion when I came to set up my tables of results. I put my results in to a table and I also did the same for the second experiment as well. I then used the results to draw my graphs and conclusions. However one of the main problems during the experiment was the amount time especially making duplicates because it took the same amount of time as the original and if you had done everything accurately then you would have to do this accurately as well. The results for the experiments can be seen as the following:
Analysis
Looking at both of my graphs for both of the experiments the general pattern is that as the molar sucrose concentration increases the change in weight decreases. If we look at graph 2 we see the increase in weight is + 0.26 g at 0 molar sucrose solution. The same is true for the next two concentrations. At 0.1 molar sucrose solution the weight increase is + 0.02 g and at 0.15 molar sucrose solution the increase in weight is + 0.03 g. This concludes to telling us that in the lower concentrations which are mentioned above increase in weight and as the molar solutions increase from 0.2 sucrose molar solution and the line crosses the iso-osmotic point the weight decreases rapidly. An example of that is a 0.4 molar sucrose solution where the change is – 0.40 g.
If we look back at my prediction, I had predicted that as the potato chip’s are put into increasing molar solution they will decrease in weight. This corresponds to both of my graphs. If we look at graph and we look at the first three molar solution you can see that the weight has increased and as the molar sucrose solutions increase the change in weight decreases. This can be shown clearly in the graph. For example at 0.3 molar sucrose solution the change in weight is – 0.22 g. Below are diagrams which show why that happened:
Evaluation
The experiment that I conducted was very successful in my opinion. I know that I obtained accurate results and was able to create good graphs. I also know that I left the potato chips in the molar sucrose solution long enough for osmosis to occur properly. However if I was to redo the experiment I would do a lot more to obtain more accurate results. Firstly I could have more concentrations. Instead of putting the potato chips in 0, 0.1, 0.15 molar sucrose solutions I could put them in 0, 0.11, 0.12 molar sucrose solution to see the effect of osmosis in such varied concentrations. This would have help to pinpoint the iso-osmotic point better.
During the experiment, cutting the potatoes was difficult. This happened because if I was cutting the potato skin I could have cut a bit of the potato of. This meant that the surface area would be effected and the overall osmosis. To solve this problem I could use a machine of some sort that would cut the potato chip to length, to an accurate surface area and an equal removal of the potato skin.
During the experiment I could have found more accurate ways of making the solutions by using a burette. This would have ensured that I have an accurate measurement of a solution. To make my measurements accurate as possible when weighing the potato chips I could have used a more accurate scale. Instead of the scale being accurate to a hundredth of a gram I could have used a scale accurate to a thousandth of a gram.
My results were good because they did show the general pattern on what I had predicted. However there were a few odd results. If we look at graph 2 we see in two places where the change in weight does not fit the general line. This is at 0.15 molar sucrose solution and at 0.35 molar sucrose solution. We can see at 0.15 molar sucrose solution that the change in weight has increased and the line which should go directly down has gone up a little. This is the same case at 0.35 molar sucrose solution. There could be reasons why this happened. One of the reasons could be that while cutting the potato excess skin of I could have cut a bit of the potato of. This would have effected the surface area and the overall osmosis effect upon the potato chip. Another reason could be that when drying the potato chip before it was put into a solution I could have dried one potato chip than the other and recorded the results. This meant that the amount of water in each potato chip would have differed from one another, and the overall osmosis upon the chip would be different. This could be the reason why I got the odd result. This reason could count for when taking out the chip from a solution. I could have taken a chip(s) out of a solution and dried one chip more than another. This meant that the weight would have been altered and the odd results occurred.
However I think the experiment was successful because if I compare it to my initial prediction it is very good and the graphs show the general line of what should have happened.
