Theory
To understand what is going on in this experiment, it helps to know some of the basic facts about what osmosis is. Below is some of my research on osmosis:
- Osmosis can be regarded as a special type of diffusion.
- Osmosis can be explained using the kinetic theory. Molecules of sugar and water ate continually moving and bombarding both sides of the partially permeable membrane. Sometimes, a water molecule passes through one of the tiny holes.
- If there was pure water on both sides of the membrane, equal numbers of water molecules would flow in both directions and there would be no overall change.
- However, in the sugar solution, large sugar molecules hinder the movement of water molecules and block their passage through the holes.
- So, more water molecules flow from the pure water to the sugar solution than the other way. The overall effect is that water flows through the membrane and into the sugar solution.
The first experiment we did was a rough test, to enable us to be able to get a better understanding of what we would be doing in the real thing. In the practise, we used the values of 0%, which is distilled water, 1%, 15% and 30%. When we came to do the real thing, we decided that this spread of concentrations was not very consistent, and if we wanted to make comparisons and draw conclusions from our results, it would be better to have a set of concentrations that were closer together, and had the same consistent difference in between them. Therefore, we decided to use the values of 0%, or distilled water, 5%, 10%, 15% and 20%. These values are all 5% different from each other, which means that it should be easier for us to compare our results, as the values will be quite close together. Also, if we are carrying out this experiment three times, we can draw up tables and graphs as well as take averages, a lot more accurately.
Prediction
I predict that in the three experiments I will carry out, that the results will show that the potato chip in water will end up being turgid and it will come off with a higher percentage gain than the potato chip in the 20% solution, which will end up being lighter than it stared and it should be floppy. I predict this because from what I know of osmosis, the potato chips in high sucrose concentrations should loose weight, as the sugar in the potato chip will diffuse through the process of osmosis into the solution, as the concentration of water is lower in the solution. Due to the same reasoning, the potato chip in water should gain weight as the water molecules will diffuse into the potato chip to equal out the water concentrations.
Preliminary Work
In the pilot test we did, the values we used of our percentage solutions were different. This means that the results we have will be different from the ones in the pilot test, though the pilot test was useful for getting a rough idea of what we were supposed to be doing and it gave us some basic results we could work off. Here are the results we gained:
In this experiment, the cork borer was 1.3 cm in diameter, which means that all the potato chips were 1.3 cm wide.
These results show me roughly what the results I gained for the real experiment show. This is basically that the potato chips in the lower percent concentrations gained more in mass than those in the higher concentrated solutions. We can use these results to further back up our conclusion.
Observations
Below are the real results we got when we were doing the practical three times. You can see from the table that we used water, and 5%, 10%, 15% and 20% solutions in this experiment.
Length of each chip: 2.9cm
Diameter: 1.1cm
Volume per tube: 20cm cubed
Red = 1st set of results
Yellow = 2nd set of results
Green = 3rd set of results
From this table, we can see that there are a few ‘odd’ results. In the first set of results, there do not appear to be any anomalous results, though without a graph, this is hard to tell. You could say, though that the fact that the mass change for the potato chips in both the 15% and the 20% are a bit close, as one is 0.01g and the other is nothing. This suggests that one of these results could be slightly inaccurate, though the best way to tell is to construct a graph, draw the lines of best fit, and then look at the line.
For the second set of results, there do not appear to be any very ‘odd’ figures, as they all show roughly what you expect them to, and they all go up, or down, instead of doing both. Until I construct a graph with the data in, I cannot see any anomalous data so far.
In the third set of results, I think that there could be a slight mistake in the figures for the percentage change in the 5% solution might be slightly out, as it is very close to the result for the 0% solution. The chip in the 0% solution gained 3.38%, and the chip in the 5% solution gained 3.27%. The next result, for the 10% solution is 0%, which suggests that one of the results might be wrong, as there is such a small gap between the first two, and such a big gap between the 5% and the 10%. However, I cannot be sure of this fact.
Analysis
From these results I can see that the mass of the potato chips in the lower concentrated solutions has increased. For example, in the first set of results, the potato chip in the 0% concentrated sucrose solution got a mass increase of 0.12g.
I can also tell that, therefore, the potato chips in the higher concentrated solutions decrease in mass. For example, the potato chip in the 20% solution in the second set of results decreased in mass by 0.15g.
See graph paper for graphs and further analytical comments.
Evaluation
Accuracy and Anomalous Results
The majority of my results seem to be relatively accurate and most of my points are on the lines of best fit I have drawn. However, there are a few results, which seem to be a little anomalous. This could be due to inaccuracy when measuring out the solution put into the test tube. Also, it is possible that some of the test tubes may have been exerted to a little bit of extra heat, or they could have been handled more than the others, which could effect the end results. The amount each chip was patted before being weighed at the end of the experiment may also have effected this. Therefore, although I cannot be accurate as to what did go wrong to make some of the results a bit anomalous, I can take a guess at some of the things that could have affected it.
Improvements
If I was doing this experiment again then there are things I could change to make my results more accurate and to try to decrease the amount of anomalous results. Some of the things I could change are:
- A more precise ruler – if I wanted to be very accurate I could use a ruler which would clearly measure in millimetres to make sure the size of each chip was almost exactly the same
- I should spend more time making sure I had dried each of the chips very carefully, as a little bit of water left on the chip can effect its weight.
- I could have been more accurate and spend more time measuring out the correct volumes. I think I may have rushed measuring the volumes slightly, so they may have been ever so slightly out, which could have effected the results
If, on a repeat of this experiment, I took care to make sure I achieved all of the above, I think I would find that my results would be a lot more accurate.
Reliability
I do not think that our results are very reliable, as the lines of best fit on my graph are not that close together. If my results were very accurate then the lines of best fit on my graph would be very close together, and there are not, though the second and third lines of best fit are closer together than the third is. Overall, I don’t think that these results are very accurate.
Although I do not think my results are very reliable, I do think that they are good enough to construct a firm conclusion, as they show roughly what I expected them to. Also, I have three sets of results, which all roughly resemble each other, so this must suggest that I did something right and that they are not totally wrong.
Further Work
If I had more time, as a way of extending this work, I could try to do an alternative experiment that might allow me to narrow down where the isotonic solution is in different vegetables. One of the vegetables I could use to illustrate this could be something like a swede or a parsnip, as they both have similar properties to that that a potato has. I could also use this to see if they absorbed as well as a potato and if osmosis would still work in these cases.