Apparatus:
Cutting Tile- to protect the work surface
Cork Borer-to cut out the potato cylinders
Potatoes
Measuring cylinder-to measure the solution
Distilled Water
Electronic scale-to weigh the potato cylinders before and after the experiment.
Different concentrations of sucrose-for the experiment
Method:
To begin with, we shall obtain 12 cylinders of potato by using the cork borer. They should be quite similar in length and size. We then measure the weight of each cylinder individual, making note of each cylinders weight. Then we use the measuring cylinder to measure 6 different solutions and pour the solutions into 6 different test tubes. The first test tube will contain 25 cm3 of just water, the second will have a solution of 0.2 molar of sucrose, the third will have a 0.4 molar, the fourth 0.6, the fifth 0.8 and the sixth 1 molar concentration of sucrose solution. All the test tubes of sucrose solution will be diluted with distilled water. So all-6 test tubes will have 25cm3 of solution. We then label each test tube with what concentration it holds i.e. 0.2, 0.4 etc. We then drop 6 of the potato cylinders into each test tube, making sure we know what the weight of the potato was before we put them in. We then leave the strips in the test tubes for exactly 20 minutes. After the 20 minutes have elapsed, we remove the potatoes from the test tubes and place them on a piece of tissue paper. We dry of the potatoes removing any excess solution. As soon as we remove the potato strips from the solutions, the osmotic activity stops. After the potato cylinders have been wiped down, we measure them again using the electronic scales. We then note the new weight of each potato cylinder. After we recorded the weight of the cylinders, we repeated the whole experiment again under the exact same conditions using the leftover 6 cylinders. This way the results are more accurate.
Precautions:
Throughout the experiment, there were a few things that could not be changed. These precautions must be taken to ensure that the experiment stays fair. These factors that will not be changed are:
- Temperature- the experiment will be done at room temperature.
- Potato-I will be using the same potato for the experiment.
- Amount of solution-each test tube will have 25cm3 of solution.
- Cork borer-the diameter of the apparatus I will be using will differ from another one so to get even cylinders I will use the same one.
- Electronic scales-I am going to keep the scales the same because the measurements may vary between different scales.
Variables:
The variable I have chosen for this experiment is the concentration of solution. I will be using 6 different solutions, Water, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar, 1 molar. This is the only variable I will be changing.
Measurements:
The main factor that will be invested in the experiment is the weight of the potato cylinders before the osmosis takes place and after they have been in the test tubes. To measure the weight of the cylinders, I will be using an electronic scale. This is because it is a very sensitive piece of equipment and can measure the weight of the cylinders both accurately and quickly. I will also use the measuring cylinder to make sure that the amount of solution used is always 25cm3.
Results:
These are the results for the experiment:
Experiment 1
Experiment 2
Graph of Results:
This graph shows the change in mass plotted against concentration. It shows as concentration increase the change in mass decreases. This used data averaged from both of the tables.
Conclusion:
After the experiment I analysed the data. Even with a quick glance I could see that my prediction was right. By looking at the graph above and the results, I could come to the conclusion that as the concentration of sucrose solution increases, the mass gained by the potato decreases. The potatoes that were in water both gained weight; the potatoes in the 0.2 molar solution gained a smaller amount of weight than those in the water and all of the cylinders in the 0.4, 0.6 0.8 and 1 molar tubes actually lost weight, the I molar cylinders losing the most. This shows that my theory, that a potato in a higher concentration will experience less osmotic activity than a potato in a low concentrate solution was correct.
Evaluation:
I think my experiment was a success because it allowed me to obtain a large quantity of results that I then used to produce a set of graphs and tables. They show my theory was correct and that osmosis is affected by concentration.
The only factor that I was not very happy about was the way that I had to cut the potatoes. The borer was very unreliable and the size and diameter of the potato cylinders were not always the same.
One way which I could improve this experiment is by increasing the time in which I left the potatoes in the test tube. I think a longer time would have allowed for more activity and possibly more accurate results. Also, if there was a more accurate process to produce the cylinders I definitely use that way. The final way that I think I could improve this coursework is by using more varied concentrations of sucrose solution such as 0.15, 0.25 etc.