Prediction and scientific explanation.
I predict that the potato will gain weight after being in the water, because of osmosis, which states that water moves from a high concentration to a low one through a differentially permeable membrane. I also predict that the water will move out of the potato tissue in the 2M solution, and the potato will lose weight. As the sugar solutions get stronger, the potato will begin to lose more weight. At the point where the external and internal solutions are the same, the mass will stay the same as it was originally. This is because of osmosis, the movement of water from a high concentration to a low one through a differentially permeable membrane.
Potato cell in water. Potato cell in strong solution.
Apparatus needed
To do this experiment I will need:
- An electronic balance
- Test tubes
- A knife
- A stopwatch
- A potato
- A range of sugar solutions (0.2M, 0.4M, 0.6M, 0.8M, 1M, 2M and distilled water)
Test tube with solution.
Plan/Method
- To carry out this experiment, first put and cut the potato into 7 pieces.
- Record the mass of each of the pieces (label them)
- Place each into a test tube
- Place each of the pieces in to the solutions (distilled water – 2M)
- Leave the pieces of potato for about 30-40 minutes.
- Remove the potatoes
- Blot them dry and re-weigh
- Record the results in the table
-
Calculate the % change in mass using the formula Percentage = weight after ÷ weight before
- Draw graph of % change v solution strengths
Safety precautions
Take care when using the knife to cut the potatoes. Wash hands! Handle glassware carefully.
Results Table
Discussion of results
The results show, that the concentration of the potato tissue is between 0.4M and 0.6M (The results where not typical, inconsistent results.).
The graph first starts to rise, but the begins to fall steeply. I predicted that the results would do this. At distilled water, the potato tissue gained weight, where as at 2M the potato tissue lost weight. When the potato tissue is the same as the surrounding solutions osmosis does not occur. Osmosis is the passage of water molecules from a high concentration of water to a low concentration of water through a differentially permeable membrane.
The result for 1M was an anomalous one. This may have been because of differences in the time spent in the solutions, or lack of accuracy in the reading of the scales.
Evaluation
If I were to repeat this experiment, I would leave the potato tissue in the solutions for a longer time and improve the accuracy in reading the scales. I would also leave all the potato tissues in the solutions for the same amount of time.
Overall, I feel the experiment went very well and wad reasonably reliable.
