I will start by gathering all of the equipment needed and laying it out. I will then use a cork borer to cut 6 slices of potato. I will then weigh these and lay them on a bit of paper ensuring that they are kept in order and all of them are the right size. Out of the six potato cylinders I have cut I have to make 18 small potato cylinders that are all the same size and weight. I will have to make the salt solution from sodium chloride and different amounts of water myself, having 6 different solutions from 0 to 2.5. I will then measure out the 6 different concentrations of salt solutions using a measuring cylinder and pour them into 6 test tubes. I will label these tubes as we go along to ensure there are no confusions over which solution is which. I will then simultaneously place 3 potatoes into each test tube and time for two days.
I will then drain all 6 test tubes of salt solution and reweigh each potato slice. I will then record the end weight and the change in weight. I will then repeat this experiment to achieve more accurate results. I will then plot the results on a graph and look for patterns.
My experiment must also be conducted in such a manner to reduce injuries. This especially occurs when handling the razor blade and forming the potato cylinders. So,
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I will place the potato on a platform or board and not on my hand when inserting the cork borer inside; if I do not, then the cork borer may cut through my hand.
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When cutting the potato tubors to equal length of 3 centimetres, I will make sure to hold it from the blunt end and be careful not to cut my fingers.
I have now conducted my experiments acknowledging the necessary safety precautions and I have used my equipment successfully without any problems; I have placed the potato on a raised platform before forming the potato cylinders preventing the chance of any injury to my hands. So on the whole I was extremely careful when using the razor blade to cut the potato cylinders to an exact length of 3 centimetres each. And finally, I have performed my experiment with the correct method I have write up above.
After performing the experiment, I have noted my observations and compared them to my predictions. I have placed 3 potato tubors in each test tube with the correct liquid inside the test tube. The concentrations of the sodium chloride solution that I have taken are 0.5M, 1.0M, 1.5M, 2.0M and 2.5M along with distilled pure water, which is 0M. These concentrations should tell me the amount of water that enters or exits the tubors; that is, it should properly reveal the experiment of osmosis.
When analysing the results, I noticed that there is an obvious pattern that falls into my predictions. I have noticed that when the potato tubors were placed in a concentrated salt solution, they decreased in mass and length. In fact, when the salt solution was more concentrated, the decrease in mass and length was greater. Therefore, there was a greater percentage difference in mass and length. I have also realized however that with the weakest salt solution, there was actually a gain in mass and length in the potato tubors rather than a loss. There was an even greater gain in mass and length when the tubors were placed in distilled water, which is 0M.
The results I have got, to my understanding and knowledge is completely fair. Because I have carried out my experiment using the right method and all the safety issues are employed in my experiment. I have used the same amount of sodium chloride solution in all the test tubes; I have left the potato tubors in the solution for 2 days in all the test tubes. And most importantly I have measured and weighed out all the potato tubors so they are all of equal length and mass.
The data that I have obtained from my experiment is shown below. I have put my results in a table so it is easier to reveal the changes in length and mass after the tubors have been placed in their respective solutions for 2 days.
I have obtained these readings after 2 days of allowing the tubors to be placed in their test tubes. I have then collected them, dried them using tissue paper and weighed each individual tubor on a weight scale.
The new mass of each tubor can then be compared with its mass reading. This new mass can then be compared with its original mass and thus with this information compiled together, I will be able to analyse what has really happened and whether the experiment of osmosis has occurred or not.
How to find out the percentage difference in mass.
With the data that I got from my experiment, it is necessary to fully understand that and analyse the results. It is also important to prove why the results are given as so. To do so, I will construct a bar graph to clearly present the data obtained from my experiment of osmosis. The bar graph clearly tells me the change in mass of the potato tubors in the different concentrations of solution; it presents the initial mass of the tubors and its final mass.
When examining this bar graph, it is necessary to take into account the scientific backing of osmosis. It is seen that from the bar graph, the least concentrated solution has the greatest increase in mass. That is, when the potato tubors are placed in distilled water, the mass of the potato tubors changes from 0.04 grams to 0.22 grams. This is because since the concentration is greater inside the cell, water must enter the cells in order to cause equalization. Now it is almost as if the potato tubors have sucked in water and it is soaked. Since they soak up with water, they will increase in mass. When the potato tubors are placed in sucrose solution of concentration 2.5M, they lose mass a lot. In this case, the mass changes from 0.04grams to -0.20g grams. This is a decrease of -0.16 grams; this is a lot of change according to my pattern because in 2.0M the decrease is only –2%. This signifies an error in my experiment; this is probably a general mistake. For example, perhaps not all the factors affecting osmosis were kept constant. For example, perhaps the temperature was not kept constant as so perhaps while the test tubes were kept aside for two days, they were differences in the temperature and so the process of osmosis took place at a faster rate and so perhaps there was a greater change in mass than expected.
Therefore, an overall statement may be made about the tubors when placed in these concentrations. When placed in distilled water, the potato tubors will increase in its mass. When placed in a salt solution of concentration 1.0M, the potato tubors will increase mass but when placed in a sucrose solution of concentration 1.5M, the tubors decrease in its mass and length. The most decrease is when placed in a salt solution of concentration 2.5M as then the concentration gradient is greater and so more water must escape the tubors in order for equalization to occur.
I have also included the percentage difference for each tubor in all the 6 different salt solutions.
With this information obtained, I may now clearly represent this on a graph to present carefully the trend that exists between these different concentrations and what its relation is to the percentage difference in mass:
Since not all the points fall into a straight line, I have decided to draw a line of best fit for more accurate results and to present the graph in the form of a straight line so that it clearly shows the relation existing between the percentage difference in mass to the concentration. From this graph, it is quite obvious that when the potato tubors are placed in distilled water to a salt solution of concentration just after 1.0M, there is a positive percentage difference in mass, indicating that the potato tubors will increase in mass. This is due to the fact that the potato cell sap is more concentrated than the surrounding solution and thus in order for equalization to occur water moves into the cells. Thus, there is an increase in mass. Nevertheless, only those potato tubors placed in distilled water have the greatest percentage difference, as there is the greatest concentration gradient; there is a greater difference in concentration comparing the external solution to the potato cell sap. Thus, more water is required to move into the cells for equalization and thus, there is a greater percentage difference. Also, when the potato tubors are placed in a salt solution of concentration 1.5M to a salt solution of concentration 2.5M, there is a negative percentage difference, which means that the potato tubors are decreasing in mass. This is because the external solution is more concentration than the internal solution, so water moves out of the potato cells in order for equalization to occur. Thus, there is a loss in mass and so a negative percentage difference.
My osmosis experiment is now completed. I have a reliable method and I have taken into account the original masses of the potato tubors and compared them with their new masses appropriately. It also allows the potato tubors to be underwater fully in their given solutions for up to 2 days so that enough time is given for the process of osmosis to occur. There are always room for improvements, and I have thought several improvements that could be suggested in order to make the method even more reliable. However, before suggesting any improvements to the methods, it is necessary to identify certain errors in my experiment.
An error in my experiment that I saw immediately is when taking the mass of the potato tubor placed in the test tube containing a salt solution of concentration 2.5M. In this case, the potato tubors had a much greater percentage difference than 2.0M, the difference was a whole –0.16g, this does not fit in my trend at all making it a anonymous result this should generally not be the case. Thus, this error could have been for several reasons, one being that the other factors affecting osmosis were not kept constant. Such factors may be the temperature; with a greater temperature the water molecules would move across more quickly and thus the rate at which osmosis occurs is increased. With a decrease in temperature, then the rate of osmosis also decreases and so perhaps the temperature was not kept at a constant during the entire experiment. Furthermore, perhaps the tubors used were irregular, that is, perhaps they were not perfect cylinders. In this case, the amount of water that enters may differ and thus the total mass of the cylinders will differ. These are the most noticeable errors.
The way my experiment could have been improved could been in many ways. The first way to improve my experiment would be to take into account these noticeable errors and overcome them to make my experiment more reliable. Now, in order to keep the temperature constant, I will keep the test tubes containing the tubors inside a stored area, where the temperature is kept constant always; this will prevent the chance of any change in the rate of osmosis and it will prevent any inaccuracies in the mass readings.
My experiment can be improved further more by using a different range of concentrations of salt solutions for more exposed changes in mass of the potato tubors when placed in these solutions. Maybe I could use 0M, 2M, 4M…. and so on. Another way to improve my experiment is by thinking whether the period of time the osmosis was taking place. Was 2 days too long or too short? I could find this out by more research. If I were to redo the experiment I would take a lot more care in accuracy of data and to expand my experiment I would carry out my experiment to the most of 3 times.
In conclusion, I have found out that when a substance is placed in a more concentrated solution, it loses water in order for equalization to occur and thus in the case of the potato tubors, they will decrease in mass. Furthermore, when placed in a less concentration solution, the tubors will gain water in order for equalization to occur and so they will increase in mass and length.
