After (Finish)
From the preliminary results I have found that as concentration decreases the mass increases this shows that osmosis has taken place. This relates to my prediction. After conducting the preliminary results I have found that it is best to use boiling tubes as the potato fits better in boiling tubes compared with test tubes as used for the preliminary investigation.
Variables:
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. Doing all the tests at one temperature will control the temperature.
For the purpose of my experiment I am going to do all the experiments at room temperature, 20 degrees Celsius.
To keep the water potential of the potato initially, it will be kept the same by using the same type of potato, which have been treated in the same way.
The mass of the potato is a dependent variable, and this means that it will be measured. Throughout the experiment: I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and to what extent.
The volume of the solution that the potato chips are kept in must be fair. The must be
totally covered in the solution, and the amount of solution will be kept the same because all the potato chips are the same size.
I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
Method
A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.2 molar, 0.4 molar, 0.6, 0.8 molar and 1 molar. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. The mass of each chip will be measured as well so that more results can be obtained. Three chips will be placed in each test tube each time so that I can take an average for each tube. I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled. The potato pieces will then be placed in the different test tubes and then left for 24 hours. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed. I do this process three times per each different solution given me an accurate average of results from which I will be able to draw a more accurate conclusion.
- Using a borer I cut the potato into chips which were around 5g to two decimal places in mass. I had to be very careful whilst cutting the potato as the borer is exceptionally sharp. I then had 10 which weigh roughly the same mass.
- Taking a test tube rack I placed 5 test tubes and then labelled them 0 molar, 0.2 molar, 0.4 molar, 0.6, 0.8 molar and 1 molar.
- I swiftly put 1 chip into each boiling tube.
- Whilst waiting I set out some paper towels with which I was going to dry the paper and I drew up a basic table for my results.
- After 24 hours I drained out the solutions in the sink and placed all the chips on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.
- I dried each chip with the paper towel and then placed each one on the scales so that I could weigh them.
- Each potato was measured accurately on the electronic scales and then the weights were recorded.
Analysis
From my graph I can see that osmosis took place in the potato. I know this as there was an increase and decrease in mass. From the graph you can see that the isotonic point is between a sugar concentration of 0.2 and 0.4. From my graph you can see that different things happen at different concentrations of sugar solution. I drew a curve of best fit to give a good indication of other points in my graph.
Distilled Water: at this concentration the percentage increase was the most (21%). This is because the lower concentration the larger the final concentrations as the water molecules pass from a high concentration to a low concentration leaving a positive percentage increase. The percentage increased by 21%.
0.2M: at this point you can start to see that osmosis has taken place as the percentage change in mass has increased slightly but not as much as the distilled water as in this case 0.2 or 20% of the solution is sugar and the remaining 0.8 or 80% is water and if there is a greater proportion of water present than solution the change in mass should be a positive percentage increase. The percentage increased by 7%.
0.4M: at this point in my graph there is a very small percentage decrease. If the results I had recorded were scientifically correct there still should be a slight increase as the concentration is 0.4 or 40% sugar and water 0.6 60%. The percentage increase was 13%.
0.6M: at this point the potato chip has become flaccid this should scientifically had happened as there is more sugar solution than the water therefore as osmosis is defined as the net movement of water or any other solutions molecules from a region in which they are highly concentrated to a region in which they are less concentrated, the percentage change as decreased in mass by 11%.
0.8M: at this point, 80% of the concentration is sugar solution and only a small 20% is water osmosis still takes place we know this as the movement takes place across a partially permeable membrane such as a cell wall, which let small water molecules through but does not allow bigger molecules to pass through. The potato chip has decreased in mass by 18%.
1.0M: osmosis is fully completed in my graph, we know this as it is the concentration with the highest percentage loss as I predicted in my prediction although the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. The percentage change was a 29% decrease in mass.
Evaluation
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. Even though one of my results was a little out the overall data I obtained was successful. The reason being that one of the results was out as I did it one two separate days therefore the concentrations were slightly different this is all to be blamed on human error. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. This way would have allowed me to also find out the isotonic point far more accurately as the one that I estimated is very approximate.
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a burette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g.
There were one anomalie result, and some were not as close to the line as others. This could have been caused by human error. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
To further this investigation I could try to find the exact isotonic point as from my graph it shows me that the exact point is somewhere between 0.4 and 0.6. To achieve this I would use a range of concentrations between 0.2 and 0.4 the concentrations I would use would be: 0.4., 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58 and 0.6. These concentrations of sugar are so precise I would then be able to find the exact isotonic point. I would create a graph which would look the same as my previous graph just zoomed in with increased concentration recordings, the recording exactly on the line would be the exact isotonic point.