Apparatus and reagents
- Test tubes
- Stoppers
- Cork borer ( of 10mm diameter)
- Metal knife
- Filter papers
- Forceps
- Digital balance( to weigh intervals of 0.01g)
- Distilled water
-
Sucrose solutions ( 0.2, 0.4, 0.6, 0.8, 1.0 mol/dm3)
- Potato tuber
Method
-
First of all, six test tubes were labelled with D.W, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm3.
- One test tube was filled with water, and the rest with sucrose solutions with their respective concentrations.
- After that, six potato cylinders about 5 cm in length were cut out from a large potato with a cork borer.
- Six filter papers were taken. One filter paper was weighed alone and then reweighed with a potato cylinder again. The difference between the two masses was found so that the mass of each cylinder could be obtained.
- This was repeated for the remaining of the potato cylinders and the masses were also noted on the filter papers. The label of the tube in which each cylinder was going to be put was also written on the filter paper.
- The cylinders were then lifted with forceps, put in their respective test tubes and stoppers were attached.
- The test tubes were allowed to stay for about two hours.
- After this, the cylinders were removed with forceps and the water was wiped off gently, using a filter paper.
- Each cylinder was placed on the balance and their masses were noted again.
Data collection
The following table shows the masses of the filter paper and the filter paper with the cylinder, to be used in the different test tubes.
Table 1:
The following table shows the mass of the cylinder after the cylinders were left in their solutions for two hours.
Table 2:
Data processing and presentation
The masses of the cylinders before the experiment were calculated in the following way:
Mass of cylinder = Mass of filter paper and cylinder - Mass of filter paper
These are the results I obtained for that calculation:
Table 3:
For the distilled water, there was an increase in mass of the cylinder, whereas for the sucrose solutions, there was a decrease in mass of the cylinders. Therefore the differences in mass of the cylinder before and after the experiment can be calculated in the following way:
Change in mass = Mass of cylinder before expt. – Mass of cylinder after expt.
The percentage change in mass can be calculated in the following way:
Change in mass of cylinder before and after expt. × 100
Original mass of cylinder
This is shown in the table overleaf:
Table 4:
Conclusion and evaluation
From the results, it could be seen that there was some error in the experiment, because the percentage change in mass did not increase in all cases as the concentration increased. This is possibly because the cylinders were cut from different potatoes, which caused a variation in the result. Another reason for the error could be that the concentrations of the sucrose solutions were not accurate.
Another method of carrying out an experiment of osmosis is to use a red blood cell instead of a potato. The red blood cell would probably increase in size when put into water. Another investigation that can be carried out is how time of keeping the potato cylinder in the solution can affect its water potential.