5. Time 5 mins on the stop-clock
6. Remove the potato chip from the solution
7. Weigh it again
8. Calculate the mass it has gained/lost and record the results
9. Repeat experiment 3 times to ensure fair test
10. Repeat all above steps using all the different solutions described above
Variables: The variables I will control will be: The volume of solution used
The length of time the potato is left in the solution
The variable I will change will be: The molarity of the solutions
Prediction: I think the solution with most water will cause the potato to gain the most weight as the concentration gradient between the solution and the potato chip will be greater. Therefore, the potato chip will take in water through osmosis more quickly than the solutions with less water. I know all this information because we have studied osmosis in lessons.
Readings: I am going to use five different solutions because this will enable me to draw a good graph so I will be able to identify patterns in the results. Because I have a limited amount of time to perform the experiment, if I used more than 5 solutions I would not have time to repeat each one three times. Therefore, I could not be sure if my results were accurate.
Results:
Water - 10ml (0M)
Water 7ml, Sucrose 3ml (0.25M)
Water 5ml, Sucrose 5ml (0.5M)
Water 3ml, Sucrose 7ml (0.75M)
Sucrose 10ml (1M)
Conclusion:
These results show that the weaker the solution, the more water passes into the potato tissue through osmosis. So, the stronger the solution, the more water passes out of the potato tissue through osmosis.
This agrees with the prediction I made because I considered the following evidence:
These results occurred because the potato membrane is a selectively permeable membrane which only allows water to pass through it. It separates two solutions; in this case the solution of the potato tissue and the different solutions I used in this experiment. Water then passes through the selectively permeable membrane from one solution to the other to equalise the amounts of water (the strength of the solution) in each. This is called osmosis. Therefore, when the solution outside the potato chip has more water than inside it (is a weaker solution) more water passes into the potato chip to balance the concentration. This is why the potato chip placed in water gained more weight because it took in more water and this made it weigh more. In the same way the solution of pure sucrose made the potato chip lose weight because the solution had much less water in it than the potato chip so water passed out of the potato into the solution to balance the concentrations.
Evaluation:
I think my results are fairly accurate because they all fit the general pattern, agree with my prediction and the evidence outlined above, and all the results are fairly similar to each other. Also I made sure that the controlled variables were kept the same. However, it is difficult to get a clear picture because the change in weight was so small. For example, many changed by just 0.01 of a gram. This means that if the scales were just slightly inaccurate it could have affected the results hugely. Bearing this in mind, if I were to do this experiment again I would leave the potato chips in the solution longer so the change would be more noticeable. Also if I used bigger chips the change would be more noticeable as well.
There were no anomalies in my results because, as mentioned above, all the results fitted the genera pattern.
To extend this investigation I could see if the size of the potato chip affected the rate of osmosis. I would keep the concentration of the solution the same and just experiment with the size of the potato. If I proved that the size of the potato chip did affect the rate of osmosis I would then perform this experiment again, but making sure each potato chip was of a set weight or size.
