Apparatus
For the experiment I will need:
20 Cylinders of potato , diameter 0.5 mm
Cork Borer
Nacl solution: o.25m, 0.5m, 0.75m and 1.00molar.
Burette to measure out the sucrose solution.
Method
I will cut lots of small potato pieces using the cork borer from the SAME potato. I wil measure the amount of Nacl to distilled water according to the varying molar solutions and then place 3 potato pieces inside it. I will leave it for 10 minutes. The temperature of the room must remain roughly the same, so it does not allow any anomalous results to appear. After 10minutes of soaking the potatoes with different solutions, I will weigh up the potatoes and produce a mean set of results.
Results
1. 0.25m- 3.68
2 0.5m- 3.51
3 0.75m- 3.49
4 1.00m- 3.32
Analysis
The results show that, in accordance with our hypothesis, the cylinders will expand when external solute concentration is low (high water concentration), and contract in strong solutions (low water concentration). This is due to osmosis, where water passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane. The graphs of % change against solution strength show that the results tend to form a curve, crossing the x axis (where there is no change in length), at approximately 0.2 molar concentration.
Evaluation
In my opinion the experiment went well. I gained a good set of results and altogether I am pleased with the investigation. The graph obtained from the results has a strong resemblance to the one in the prediction. This suggests that the experiment was fairly accurate. Although 3 repetitions of each concentration are sufficient, there was a possible anomalous result (circled on graph). This part of the investigation would need to be repeated. A possible factor affecting my results is that although the cylinders were taken from the same potato there is no guaranteeing that the density remains the same throughout the potato. Another factor is that the potato from which the cylinders are taken could be abnormal - this could be prevented by amalgamating sets of results, for example of a whole class, where each experimenter used a different potato. I think that three sets of results was a good number. However, I think that in order to improve my results, the last concentration (1 moler) needs to be retaken as it is an anomalous result.
Further work could be carried out to include concentrations that increased in 0.1 M rather than 0.2M. This would increase the accuracy and improve the graph. Other investigations could include using different varieties of potato or different plant tissues e.g. carrot.
