Safety
Preliminary experiment
These results were taken after 10 minutes, which is a third of the time that I will use in the actual experiment, this may have affected the results. I predicted that the 100% salt solution would have the greatest loss in mass but from these results the 40% salt solution has the greatest loss. However these results are true to my prediction in one way because the 0% solution has the greatest gain in mass. I think the reliability of the results could be improved by using an average and by increasing the time to 30 minutes, which is probably the least amount of time that the osmosis process needs to work.
Method
From my pilot test I found that I should use ten different molarities in the actual experiment, in order to get a reliable and wide range of results. There will be one variable in this experiment, the different molarities of salt solution.
I must keep the potato samples the same length (2cm) because if one potato sample is longer than another it will have a larger surface area therefore the osmosis process would be quicker.
I will use the same potato because many factors such as age may affect the experiment.
An accurate amount of salt solution must be used to ensure the concentration is exact. I will do this by using a syringe to measure the amount needed.
As each test tube is filled up with the different molar solutions, the syringe may contaminate each solution therefore I will wash it after each time it has been used.
To make the experiment as accurate as possible I will take an average out of the three results.
The temperature may affect the reliability of the results, for example if it is too high it may speed up the process. To prevent this I will keep all test tubes in the same places where there is a controlled temperature.
- Set up test tubes, three for each molarity %, making sure that they are labelled.
- Prepare solutions for each molarity 0% to 100%.
- Prepare potato samples, cut out cylinders of potato using the same cork borer then cut to 2cm long using a scalpel.
- Immediately weigh each sample, record the results and then place into the solution.
- Set the stop clock and leave for 30 minutes.
- Remove samples, put onto paper towels to wipe off excess water.
- Re-weigh samples and record results, then work out the change in mass.
Apparatus List
3 medium sized potatoes
1 size 6 cork borer
3 test tube racks
1 scalpel
Distilled water
2 paper towels
1 measuring cylinder
1 molar strength salt solution
11 test tubes (large) x3
Results
I have taken three sets of results so that I can find an average, as replicates enable me to be more accurate with my results and give me more evidence to prove my prediction from.
When obtaining my results, I reset the balance, so that it would read zero. This was because if the balance had not been reading zero it could have affected my results dramatically.
Analysing evidence
I have found that my prediction was correct, that the potato chip with the greatest weight loss will occur in the 100% salt solution and the greatest weight gain will occur in the 0% salt solution. Also from my preliminary experiment I predicted that if I left the experiment for 40 minutes rather than 10 minutes it would increase the reliability which it did, as all results followed the same pattern. The potato cells took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it was surrounded in.
There is a pattern on my graph, and this is, as the morality of the salt solution increases, the change in mass decreases. The gradient does change in my graph. It gets less steep as 'x' gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each morality are becoming closer and closer together. All of my results lie close to my best-fit line. This shows that my results are fairly reliable. There were not really any anomalous results, apart from the 20% solution in the third set of results which does not follow the same trend. As the other results are increasing in the difference in mass, it has decreased. This may be because we weighed the 20% result as the 30% result or because of another human error. Also some results were not as close to the line as others. This may have been caused by human error, or one out of my three results could have been inaccurate.
Evaluating evidence
The first thing I could do next time would be; to keep the samples in a water bath at a set temperature, this would mean that I would know the temperature would be the same for all solutions. I followed the safety instructions throughout my experiment so I know it was performed safely.
My results agree with my prediction, which was when you increase the molarity of the salt solution, the mass of the potato decreases. This is due to osmosis; the movement of water molecules through a partially permeable membrane, from a region of high water concentration to an area of lower water molecule concentration. This meant that water molecules left the cell sap and went through the potato cells partially permeable membrane and into the surrounding salt solution.
When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time.
If I was to repeat the experiment I might well increase the time of the experiment, leaving each set for a longer period of time, this would probably lead me to better results, because the osmosis action would reach its maximum capability, and therefore tell me how much water could be transferred for each solution.
I could extend my enquiry by testing the percentage change in mass with morality using a different substance. By this I mean using a different vegetable, perhaps celery. Then I could find out whether osmosis occurs with the same patterns and trends with any vegetable.
