Osmosis Investigation

Results

Each of these results is equivalent to the volume of an equal mass of water. Because water has a relative density of 1, this means all volumes are in cc.

Conclusion

We can therefore see that there is a definite pattern in the volumes of the different potato cylinders, and that it does indeed correspond with the prediction established on the previous page. However, the lack of one piece of data does seriously compromise the usefulness of this data. After having carried out the experiment, I compared the results with the original mass I had taken before putting any of the potato cylinders in the beakers. While my results made sense compared to each other, they did not make sense in relation to the original measurement, 0.28g. This error will be discussed in greater detail in the evaluation; here, we need simply concentrate on the implications of this. Because we have no original measurement to go from, we cannot effectively say how each of the different concentrations has affected the potato. Instead, we are left to attempt to infer the starting point from the data we have collected, a much more tricky task. It is clearly obvious that we cannot obtain the answer from the raw data; without an origin, we do not know which two pieces of data we are to find the centre of, and thus we get no-where. The one major possibility is that the graph may show a curve rather than a straight line- i.e., as the concentrations increase, they reach a level where no more osmosis can happen, and thus appear on a par with the values before them. If we were to find evidence of this, then the start point would logically be the centre of the curve. This, however, depends greatly on whether out range is wide enough to encompass this possible curve. We cannot go much lower in concentration than 0, but what if the centre of the curve lies up around 0.75M – we would not have enough data to find the centre. We must therefore analyse the graph of the results.

This is the kind of curve we must look for in the graph- evidence of osmosis happening more rapidly in the centre (near the original volume and concentration of the potato), and less rapidly at the ends, when little more water can move either way.

It is worth noting at this point that visual evidence demonstrates that the centre point must lie within our range of results- some of them were clearly shrunken, whereas others were much larger than before. The visual evidence, however, was not enough to deduce the actual centre point.

This graph shows the averages of all my results as displayed in the above table. Despite the possible presence of a slight curve at the far bottom of the graph line, the fact that this rises above the previous results makes it slightly dubious, and in any case we have no curve on the opposite end to find the centre from. The graph, therefore, gives no clues about the possible start point for the graph. However, there is a final method we may try to employ to find the original volume. If, possibly, results had cancelled each other out to create the average as used in the above graph, it is possible that one of the strings of results may give a positive curve. We shall therefore look at the graph showing each of the individual measurements.

It is further worth noting that there is no significance in relationships between measurements collected along a line; this is simply the order in which I entered then into the table. However, this is generally irrelevant, because we see no curve on any of the lines- to be absolutely sure, we would have to draw graphs with every alignment of the different measurements (i.e. the “0” value on R1 with the “0.5” from R2, and so on); however, I believe any data requiring such manipulation of the results would be worthless, and worse, misleading; therefore this has not been done.

We shall finally look at the more trivial point of whether the results agree with the prediction. In short, they do. The greater the concentration of sugar outside the potato cylinder, the lower the volume of the potato, and the lower the concentration, the greater the volume. A subset of my prediction (not mentioned above); that the osmosis process would trail off as the concentrations got more extreme, would have been indicated by the curve we were looking for earlier, and was therefore not supported. However, I still believe that the prediction was valid, and that the lack of evidence is caused by not having concentrations extreme enough to begin to show it.

Evaluation

I believe that the experiment was, overall, a success. The results generated did fit the pattern of osmosis, and were actually quite definite- I did not have to play with them a great deal to find any evidence; they immediately fitted the pattern. The results for the 1M concentration were slightly anomalous; they unfortunately fit into that space where they are far enough out to cause concern, but not so strange that we can immediately classify them as wrong. We are therefore left to speculate on these measurements. I believe the most likely cause for this is a problem with the solution; perhaps I measured it incorrectly, or the solution I used was slightly dilute.

I was particularly pleased that my alternate method had generated such good results. I was previously slightly worried that as I had used a method I proposed myself, rather than the original one, my results would make no sense due to the method of measurement being faulty. The result was almost the opposite; I believe that, if anything, my results were more accurate than those of people who had measured the length of the cylinder. This was my original intention for the alternate method, and I am quite satisfied that it worked.

As mentioned above, the major problem in my experiment was that with the initial measurement of the potato, and this seriously compromised the value of my results. I am still unsure about the cause of this problem; as far as I know I carried out the measurements correctly. I can only assume that I am wrong about this, or that the particular scales I used to measure the volume were faulty.

The comments I make about how to improve the experiment will be imminently predictable; more time and more resources. A single hour is, frankly, insufficient time to prepare and implement an experiment such as this, especially combined with insufficient resources. Were I to have had more time, I would have made measurements on each and every potato cylinder before using them in the experiment, something that would have both protected against the problem I encountered, and given me more useful results, because I would have been able to identify varying amounts by which each specific potato had grown/shrunk.

Aside from these improvements, if I were to repeat the experiment, I would do it with more potato cylinders using smaller intervals between the different concentrations, and I would have extended the range to look for evidence of the curve in the graph.