Prediction: I think that the higher the concentration of sucrose the larger the amount of water will be transported into the potato cells as osmosis is the net flow of water through a selectively permeable membrane from a high water concentration to low water concentration. This means the water molecules from a low sucrose solution will move water molecules but not sugar molecules through the potato skin into the potato cells making it turgid and absorb water molecules from the solution surrounding it. In a higher concentration of sucrose in a solution the same process will occur but less water can be transported as there will be more sugar and less water meaning that excess water from inside the potato cells will transport from the cells to the high sucrose concentration solution which will cause the potato to shrink and become flaccid.
Plan
Apparatus:
1 potato
Cork borer
Sucrose solution
Distilled water
10 Test tubes (boiling tubes)
Burettes
Scales
I will be measuring the mass of the potato piece after osmosis has occurred in the test tube, after the process has happened I will take out the potato and dry it to ensure excess water is not added to the results which could produce an anomalous result, I will then place the potato piece onto the scales and note the results on a table.
The control variable in my experiment is the water that will be lost during the test, the evaporation will be controlled using film secured on the top of each of the test tubes to prevent uneven loss of water from disturbing the experiment.
The independent variable is the alteration of the concentration of the sucrose and distilled water in the solution that the potato will be suspended in. I will select different concentrations that will provide the most efficient results for me to observe the effects.
To make a safe investigation I will have to make sure to take necessary precautions when using the cork borer to cut the potato into useful strips that will fit into the test tubes. To produce a fair result we will repeat each test to find an average.
Fair Test
To obtain accurate results fair testing should be considered. If this experiment is not a fair test, we will be obtaining the wrong results and the experiment will be a failure.
We will have to get the measurements and the weights of the solutions and the potatoes as accurate as possible.
Also, we will make sure that every chip is totally submerged in the solution because then every chip has an equal amount of solution around it. When using the balance, we will make sure that the balance is reading zero and after the experiment taking the reading to the nearest 2 decimal places.
Carrying out the experiment in a constant temperature during each part of the experiment and therefore we will leave each set of test tubes on the same place every time so that each tube is in the same atmosphere. Another important factor of a fair test is to make sure that every set of test tubes is tested for the same period of time - 24 hours.
It is also very important to use solutions with the exact concentrations of sugar otherwise it would affect our results.
Safety
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration.
We will be using a very sharp knife, which could injure someone if it is not handled properly. Also, we will make sure that we do not drink the solutions and wash our hands after handling them. Also, we will remember all the basic rules of working in a lab such as tie back long hair, not running etc.
Method:
- First we will place a tile on the work surface to prevent damage, we will use the cork borer to punch equal chips of the potato, we will need to cut 10 pieces and prepare them by weighing each piece and recording the weight.
- We will measure out the correct solutions of each substance, the distilled water and the sucrose solution. Once carefully measured out the potato pieces will be placed in the test tube with the correct measurements and they will each be labelled showing which solutions each has and either it is the original or the repeat.
- We left the test tubes to work, as the effects will not be seen at once.
- Once a change has occurred we will take each potato piece out of the test tube and after patting excess water off from the potato we will weigh it again, and note the difference in a table.
- We will finally clean all the equipment and safely store them.
- After 24 hours, we will take all of the potato pieces out of the test tubes, so that the osmosis stops, and we will put the potatoes onto another piece of dry towel.
- Then we will weigh each potato piece again and record the results. We will repeat the experiment so that we can make sure that all our results are similar, and so that we will be able to take the average of the experiments. Repeating the experiment is important, because we will be able to receive valid results, and look for any anomalous results.
I have recorded the raw data in the table below:
I have calculated the percentage change in mass using the equation: (Change in mass/ original mass) x100
I have a table of the molarity of the sucrose solution:
Table of manipulated data
Evaluation:
Having researched osmosis and conducted a preliminary experiment, I think that my final experiment was appropriate for investigating the task set and provided us with reliable results. There were no obvious anomalies and, although some results slightly contradicted my prediction, the averages supported my hypothesis.
I think the procedure, which we used, was suitable and worked well. The evidence that it provided us with was sufficient to support my prediction and to draw conclusions from. However, there were areas for improving the accuracy of our results: if the potato chips did not rest against the sides of the test tubes then they would all have the same surface area. This is the same for the potato samples that float therefore exposing themselves to air and the samples that sink stopping osmosis occurring on the areas that are touching the bottom of the test tube. Human error could have been reduced by taking more accurate measurements and cutting with more accuracy. This could be improved by using a tool, which could be set to a set length to cut the potato.
To get a wider perspective on this subject, I would like to repeat the experiment again but using a different vegetable or fruit, for example, with a carrot or an apple to see if osmosis affects them in the same way as it does potato. I would also widen the range of sugar concentrations to include 1.1M 2M. Moreover, I would like to see if and when the cells reach a maximum and minimum weight.
Temperature could also be changed, for example the samples could be placed in different test tubes at different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 3 potatoes could be placed in test tubes at 10oC, 20oC, 30oC, 50oC and 60oC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would gain the most weight. This is because at high temperatures the water molecules would move faster and therefore equal the concentration faster. A preliminary experiment could be set up beforehand to find out how long the experiment should be kept going because if the concentration of the potatoes equalises then the weight of the potatoes will be almost exactly the same.