We performed an experiment with a visking tube; this was our “areliminary experiment”. We had to put a sugar solution and a capillary tube into a visking tube, (which was partially permeable); this was put into a beaker filled with water. We also had to make a prediction for this experiment. I predicted that the water will force its way into the visking tubing, causing the volume in the tubing to increase then forcing the sugar solution up the capillary tubing.
Essentially what I am saying is that as the concentration increases, so will the amount of mass lost by the potato.
Key Factors
In this investigation the key factors which are able to change, are the concentration of the sugar solution surrounding the potato; the size, length, weight and surface area; the shape of the potato and the circumference. The room temperature or whether or not you cover the tubes or beakers with cling film.
Fair Test
To create a fair test, I am going to make sure that the volume of the sugar solution is the same each time, at 10ml. I will keep the size and weight of the potato the same, also the type of potato will remain the same. I will control the size of the potato by using the same size of cork borer and I will cut the lengths the same.
Reliability
I have tried to make the results as reliable as possible by using distilled water to eliminate any sort of variation in the water. Also the measuring cylinder was washed and cleaned in between measuring to prevent the next mixture being inaccurate. The same type of potato was used etc (see fair test). I will also repeat the experiment three times and take the average measurement, in an attempt to get the most reliable and accurate results possible.
Modifications
I choose do each solution three times as this would give me a better average and make my experiment more accurate. I also decided to measure each potato carefully with a ruler and electric scales to get a precise weight. Other than this I did not change anything as a result of my preliminary experiment.
Evidence
I measured 5 different concentrations of solutions to make sure that I got a significant set of results. By taking the 5 different concentrations my work was varied enough to get a fair set of results due to my preliminary work. Also testing it three times allowed me to identify any differences that may have occurred and I would have been able to take them into account.
Accuracy
I have ensured maximum accuracy by using smaller measuring cylinders and making sure not to contaminate all the equipment. Also, and most crucially, I am repeating the experiment 3 times so as to obtain maximum accuracy and then taking the average.
Identifying Tends
I was able to identify certain trends from the evidence. The pieces of evidence which relay my findings are the graphs I have produced. The one entitled "Average Change in Mass against Concentration". The graph quite clearly shows the relationship of how increasing the concentration of the sugar solution forces the potato to lose more mass. This trend can be summarised as: If you increase the concentration of the sugar solution, the mass of the potato will decrease as well. The graph entitled “Change in Mass against Concentration" makes me think my results were accurate as the 3 lines are very close together. This indicates to me that I have kept within a good accurate and consistent level. From both graphs I am able to find that there is no directly or indirectly proportional link to the loss of mass and sugar solution, but there is a relationship that as you increase the concentration the amount of mass change increases. I did however notice that in the middle of the graph the line was straight, but it started to tail off towards the extremities of the concentrations used. I feel this was due to the fact that the cell walls were unable to expand or contract anymore, so therefore put up more resistance and prevented the shape from being changed more.
Conclusion
The above graph gives us the information from the table; one of the things that portray is the rapid concentration increase. This statement is backed up by my results, in both the table and the graph.
From my investigation I can conclude that it was accurate, due to the graph which falls in line with a certain degree of consistency.
I have found out and can prove that as the concentration increases so will the amount of mass lost by the potato. All of this evidence backs up my initial prediction. "Essentially what I am saying is that as the concentration increases, so will the amount of mass lost by the potato”.
The graph starts off by gaining mass, but then it starts to decrease in mass. So, we can understand that the direction of osmosis changes to being from the potato to the solution, when it started being from the solution to the potato. As the water particles pass out of the potato, it starts to lose mass.
No osmosis is taking place at 0, this means that the potato neither looses nor gain any mass. When osmosis occurred in this case, the water molecules moved from the potato to the sugar solution. The water molecules made up a large part of the mass of the potato; this is why the potato lost mass during osmosis, as it lost many water particles. This can be proved from the definition of osmosis: “the movement of water molecules from an area of high concentration to an area of low concentration through a semi-permeable membrane”.
When the concentration of the sugar solution and the concentration inside the potato are equal there will be no mass change in the potato, because one of them is not higher in concentration than the other.
Although the rate of osmosis was higher as the concentration increased, it was also a high rate of osmosis when the concentration was lower, but in the opposite direction. Although I was partially correct in my prediction, it would be easier to be more specific when thinking about the outcome.
I would be interested to go further with the concentrations. I did expect it to allow a certain amount of loss or gain of mass. All in all I would say that the experiment was well conducted and to a good deal of accuracy.
Evaluation
I do believe that my results were accurate. The proof for this is in the graph I have drawn, this shows results from all of my experiments, and as you can see all are consistently together. This proves that I am consistently accurate with my experiments. There is little chance that they were all wrong as they were done together so it was fair.
There are however many places and ways that errors could occur. First starting with the concentration; it was possible that the concentration of the sugar was not already precise when I got it. Also there is the large possibility that I measured the quantities wrongly, by only measuring it a couple of ml more or less made the experiment unfair. To make this aspect more accurate I would use a smaller measuring cylinder than a 20ml one and be sure to measure from dip in the liquid. This allows for any remainder of liquid left in the cylinder after pouring. Also a major factor was the cutting. I could have easily left a larger surface area on one than the other. Therefore one would be at an advantage as a larger surface area induces more osmosis to occur. One way to avoid this would be to use complicated machinery to weigh and cut the potato; although beneficial, this wasn't practical, so just taking extra time and care with the cutting would make it more accurate. I did test a wide range of concentrations – this made me able to obtain a more accurate result. I could also experiment with exposing the same weight pieces, but with different surface areas. This would be interesting to do, as I could imagine the results would be ever so different.
If I was to repeat the experiment again then I would go to a higher concentration to see what happens in relation to this experiment, and see exactly how much osmosis is able to occur. If I did more varied concentrations by adding as much sugar solution; the reason for this is I feel it would provide me with more accurate results to base my graph and theories on. Also I would like to see how the surface area would affect osmosis, for the reason this is, I feel that it would be interesting to know what affect it has and to compare it to the other set of results I obtained.
