Prediction:
The tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato. The speed at which osmosis occurs depends on the concentration gradient of the two substances in the solution.
So, when the water concentration is lower in the potato cell, the water will go inside the potato cell, and the potato will gain weight. If there is higher concentration of water in the potato, water will go out of the potato and into the solution through the semi-permeable membrane. If there is very little difference between the two water concentrations, there shouldn’t be such a big change in mass of the potato chip.
My Prediction Graph shows that the potato should grow more in a diluted solution more than a concentrated solution of salt. It should even shrink in a solution if it is concentrated enough. Points should be plotted equally in the growth region and the shrinkage region. A line of best fit should hopefully, in an accurate and error-free graph, be a straight line. The isotonic point should also possibly a realistic percentage from 10% - 35%.
Variables:
- The concentration of sugar and water in the solution.
Constants:
- Length of potato chip.
- Surface area of potato chip.
- Volume of solution.
- Same potato used to cut the potato chips.
- Temperature.
- Time left in solution.
Method:
- I cut the potato into chips by using the same cork borer each time, so that the widths of the potato chips were all the same.
- I measured the length of the potato chips, using a ruler, and then I cut them down to 2cm with a scalpel on a cutting tile.
- I then weighed the potato chips and noted their masses.
- The salt solutions were made by adding different amounts of salt to the same amount water in different beakers.
- I put the weighed potato chips in the salt solutions.
- After an hour, I took out the potato chips and weighed them and once again noted down their masses.
- I then did the same experiment again with the same method using different potato chips from the same potato.
- After the repeat experiment was finished, I took the average of the masses taken at the starting and the masses taken at the end.
- The change in mass was calculated by subtracting the start average mass from the end average mass.
- The percentage mass was calculated by:
Change in Mass
Average start Mass
Equipment:
Results:
Conclusion:
By comparing my actual graph to my predicted graph, you can tell that my experiment went drastically wrong.
Evaluation:
The experiment suffered from many errors and limitations. These may of caused the anomalous points on the graph and the inaccurate results.
When I was doing the experiment time was against me. I had limited time to do the experiment, which caused lots of problems with the experiment, and increased the amount of human-errors I had would have made.
When I weighed the potato chips, and because I had little time, excess water from the potato chips, was left on the scales, which added weight to the next potato chip I weighed.
I found it very difficult to cut the potato chips to the correct dimensions. Firstly, using a cork borer, I had to bore holes in the potato. After a while this became increasingly difficult and tedious as there was a lack of space on the potato to bore the holes, and I wouldn’t be able to use a new potato because then it wouldn’t be a fair test. Then, using a ruler, I had to measure the length of the potato chips to 2cm and cut them using a scalpel, which consumed time that I didn’t have and also human-error played a part in making sure that the lengths of my potato chips weren’t very accurate, not forgetting the pressure under which I was in. Handling delicate potato chips of this size also proved to be quite a challenge.
Since my results were wrong, the whole graph was obviously wrong. However, there is an anomalous point in my graph. To have an anomalous point in my graph must mean it is different, and in terms of right and wrong, it must be a correct point.
The first point I plotted, with a ring around it, is the anomalous point, since it is the only point that matched my prediction.
It would be hard to draw a line of best fit unless; the two points that are circled in blue are omitted. The line of best fit you can see in black has been done omitting the points circled in blue.
The potato we used was new and fresh. Since it was fresh, the cell would obviously be turgid, which could prevent the process from reaching it’s maximum potential and thus preventing the results from being error-free.
Instead of using fresh and new potatoes, which can alter results, I should of used an old potato that would be flaccid and so be able to perform osmosis more efficiently.
Doing experiment under little or no time pressure could easily bring results to be more accurate, and also the potato chip would be able to be left for a longer period of time so osmosis in the potato chip can properly take place. Instead of putting a single chip in a test-tube, it would be netter to use two or three chips in a test-tube, which would give much more accuracy if an average were taken.
Each time I had finished weighing a potato chip, I would have enough time to wipe the weighing scales with a tissue.
It would be good idea to use a different variety of vegetables in this experiment instead of only potatoes and also the solute in the experiment, could also be changed. For instance, you could use sugar instead of salt. Using different solutes and vegetables can also be able to answer the question, Do the size of the particles and the membranes affect the rate of osmosis?
Machines have always been more efficient than humans and are faster and more accurate than humans in performing work. Machines can also have some use in this experiment. They can be used to cut the potato chips very accurately down to the nearest tenth of a millimetre. Even to make the solution they can be used. Heating the solution first would allow all the solute to get dissolved, and then letting the solution cool down would make sure that only the maximum amount of solute could be dissolved.
In the interest to make the hole borering much easier, it would be good to use a much larger potato.
