As my graph seems to lie more between the 0M and 0.5M marks, I will do my experiment using that range of data. For example, I will use 0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M and 1M. Covering the top may help to prevent evaporation, so in m actual experiment I will cover the test tubes with bungs or cling film. As the preliminary experiment took a long time to set up and to weigh the chips et cetera, I will organise the equipment beforehand and this will save me time and I will be able to carry out the experiment more efficiently.
As I only did one experiment, the results are likely to be dubious and inaccurate. In order to ensure that my test is accurate, I shall repeat it three times and take an average. Instead of using one chip for each test tube, which will use up seven and doing the same procedure again two more times, I will put three potato chips for repeat in a test tube. This means that I will only need to use seven test tubes overall. I will use coloured pins to distinguish which set of repeats the chips come from. I also thought whether or not I should include the pins, while weighing the mass of the potato chips and decided to keep them in whilst weighing them both times. This will not affect the results, as the percentage change in mass will be noted. This is a timesaving method and will be more efficient when taking results at the end of the experiment.
Fair test:
Apparatus:
Risk Assessment:
Diagram:
Planned method:
- Push cork borer through the potato, cutting into long cylinders (with a scalpel) of about 10mm.
- Label seven test tubes: OM, O.1M, O.2M, 0.3M, 0.4M, 0.5M and 1M.
- Place the pins in the necessary potato chips and weigh them all.
- Cover the test tubes with a bungs and leave in a cool place for 50 minutes
- Take the potato chips out from the sucrose and blot them in kitchen paper to absorb any sucrose.
- Weigh them again and take an average reading
OBTAINING EVIDENCE:
Method:
- I took a potato and cut out 21 cylinders from it, using a cork borer.
- After laying all 21 pieces of potato on a tile, I used a scalpel to cut them down to 3 cm in length.
- I put a blue pin in all the potato chips in the set of potatoes laid out for my second repeat and an orange pin in the chips for the third repeat.
- I measured each potato chip separately on an electronic balance and recorded the results in a table.
- I took 7 boiling tubes, put them in a test tube rack and placed amounts of sucrose solution and tap water as shown in the table above. I used measuring cylinders and syringes in order to obtain accurate measurements.
- I placed 3 potato chips in each boiling tube; the orange pin, blue pin and potato chip with no pin were put in the same boiling tube, as they resembled the repeats.
- I then covered the boiling tubes with bungs to prevent evaporation.
- After an hour and 15 minutes, I took out all of the potato chips and blotted the solutions of kitchen paper.
- I then measured their mass again and recorded the results in my table.
- There was no need to repeat the experiment as I did all three repeats in one experiment.
Precautions:
- As was stated in my planning section of the coursework, I had to keep all of the different non-variables the same, to make sure that none of them affected the results of the experiment in any way.
- I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potato.
- I had to be very careful when cutting the potato chips with the scalpel, as it was very sharp and could easily cause a serious wound.
- The measurements of the sucrose solutions and water had to be precise, as not to change the outcome of the experiment and the results.
Results table:
Graph
ANALYSIS:
The graph shows a line of best fit over a 90-minute period. Because the line is not straight and does not pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional. But there is a definite trend, as shown on the graph. The line of best fit shows that as the sucrose solution becomes more concentrated, the percentage change in mass of the potato chip decreases. This can be shown by the gradient becoming less steep as the concentration of sucrose solution increases.
Although my line of best fit came out quite well, I didn’t get any negative results, which may indicate. My results are fairly accurate as they are plotted quite close to the line of best fit. However there are two or three anomalies, which don’t seem to follow the line of best fit. These anomalies may have occurred due to flaws in the experiment, for example, uncontrolled variables such as light, temperature et cetera.
Conclusion:
Overall my experiment was successful, even though I predicted that I would have some negative results and I didn’t. However, the potato cells took in or released as much water as necessary. Also in my prediction, I thought that my line of best fit would run through about 0.5M of sucrose, but it went further than that. I expected my results to reflect my prediction, but it wasn’t as I had planned it to be. My results in the 0.1 to 0.5M range came out quite well, but there were a few anomalies. My graph and results show two main points:
- That osmosis took place in the experiment
- As the molars increased, the average percentage change in mass of the potato chip decreased.
The results show that the potato chips increase in mass when they are placed in solutions with a high water concentration. And although my results have not shown this, potato chips placed in solutions with low water concentrations should decrease.
This shows that osmosis occurs in all living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration), the water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid. If done with potato cells the cells would increase in length volume and mass because of the extra water.
If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.
The greater the concentration of water in the external solution, the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution the greater the amount of water that leaves the cell.
However, there will be a point where the concentrations of water inside and outside the potato cells are equal and this is when equilibrium is formed. At this point there will be no change in the length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.
Evaluation: