To investigate how changing the concentration of salt solutions affects osmosis in a potato chip.
COURSEWORK: OSMOSIS
Aim:
To investigate how changing the concentration of salt solutions affects osmosis in a potato chip.
Hypothesis:
Increasing the concentration of salt in a solution increases the amount of osmosis occurring.
Theory Behind the Experiment:
Dictionary Definition of Osmosis: Diffusion of fluid through a semi-permeable membrane.
Osmosis will occur from a high concentration to a low concentration. It usually involves the movement of water, but can also involve the movement of sugars and salts.
Osmosis will change a cell's shape, whether it is Flaccid, or Turgid.
A flaccid cell will usually gain water through osmosis, and a turgid cell will probably lose water.
Equipment Needed:
Boiling Tubes (5)
Ruler
Salt Solutions (4 Different)
600 ML Beaker
Weighing Scales
Distilled Water
Bread Knife
Thermometer
Measuring Cylinder
Glass Rod
Potato Chips (15 equal)
Core Borer
White Tile
Method:
* Take all equipment needed (above).
* Cut the potato into two using the bread knife.
* Place each potato chunk, flat end down, onto the white tile.
* Using the core borer, bore out 15, equal-sized, chips.
* Cut each chip down to an equal length, using the bread knife and ruler.
* Weigh the chips, in sets of 3, and then divide the total weight, of the 3, by 3 to determine the average weight of the chips.
* Measure, using touch, whether the chips are turgid, flaccid, wet or dry.
* Place the chips, again in sets of 3, into the boiling tubes.
* Add the salt solutions and distilled water to the boiling tubes.
* After 30 minutes, remove all the chips from their tubes, and re-measure their weights, lengths and textures.
Fair Test:
To assure the fairness of this test, we should:
* Use the same core borer for each chip bored.
* Use the same volume of solution or water for each test tube.
* Make sure each chip comes from the same age of potato (older potatoes will have less water originally).
* Take three results, and average them, to minimise error.
* Make sure all chips are of the same length.
* Make sure none of the chips have skin (skin provides a barrier against osmosis).
* Cut chips so their edges are square to each other.
Independent Variable:
Molarity of the salt solutions.
Dependant Variable:
Length, mass and texture of the potato chips.
Preliminary Results:
Temp. of Room: 23 Left for: 12 mins. Volume of Solution: 10ml
Solution Molarity
(M)
Original Mass (g)
Average
Original Length (mm)
Original Texture
Final Mass (g)
Average
Final Length (mm)
Average
Final Texture
...
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* Make sure none of the chips have skin (skin provides a barrier against osmosis).
* Cut chips so their edges are square to each other.
Independent Variable:
Molarity of the salt solutions.
Dependant Variable:
Length, mass and texture of the potato chips.
Preliminary Results:
Temp. of Room: 23 Left for: 12 mins. Volume of Solution: 10ml
Solution Molarity
(M)
Original Mass (g)
Average
Original Length (mm)
Original Texture
Final Mass (g)
Average
Final Length (mm)
Average
Final Texture
0.0 (Control)
.29
20
Turgid, Wet
.4
22
Turgid, More Wet
0.5
.29
20
.21
20
.0
.26
20
.07
8
More Flaccid, More Wet
.5
.18
20
0.91
7
2.0
.17
20
0.90
8
Preliminary Evaluation:
On the whole, the experiment went well; we got results that make sense. The big problem that we got during the experiment is that the experiment suggested that there was no osmosis occurring at 2 different points during the experiment The mass results suggest that no osmosis occurs at 0.2M, but the length results suggest that no osmosis occurs at 0.5M. Whether this is a display of error, or supposed to happen, we don't know, and we will not until we do the final experiment.
If we are to find out, though, we must:
* Increase the volume of solution used, from 10ml to 15ml, because 10ml did not fully cover our entire set of chips, and so the averages would be affected.
* Measure and cut all chips one-by-one, instead of as a whole, so we can ensure their length, and not just assume they are the right length.
* Because of time restraints, the preliminary experiment lasted 12 minutes. To ensure all the osmosis takes place, we will increase this to 30 minutes.
* Ensure all chips are kept in a similar environment, as heated environments will cause water loss, and wetter environments can cause more osmosis to happen.
Prediction:
Using the preliminary results, I predict that when you increase the concentration of salt in a solution, you decrease the amount of osmosis occurring.
Eg. In the preliminary results, at 0M of salt in a solution (distilled water), mass increased by 0.1g, and length increased by 2mm, but at 1M of salt in a solution, mass decreased by 0.19g, and length decreased by 2mm.
This pattern shown in my preliminary results would be because the concentration of water in a solution has most bearing on the amount of osmosis, not salt concentration. So, as we increase the concentration of salt, we decrease the concentration of water.
I also predict that no osmosis will occur between 0.2M and 0.5M, because that is where the preliminary results suggest no osmosis takes place. Any solution with a higher concentration of salt than that would have too low a concentration of water for osmosis to work, and indeed, osmosis will actually occur in reverse, taking water out of the chip.
Final Results:
Temp. of Room: 21 Left for: 30 mins. Volume of Solution: 15ml
Solution Molarity
(M)
Original Mass (g)
Average
Original Length (mm)
Original Texture
Final Mass (g)
Average
Final Length (mm)
Average
Final Texture
0.0 (Control)
.57
20
Turgid, Wet
.76
21
More Turgid,
More Wet
0.5
.59
20
.38
20
.0
.63
20
.55
20
More Flaccid,
More Wet
.5
.61
20
.34
9
2.0
.60
20
.36
8
In order to save time, the chips were weighed in sets of 3, so there are no individual weights. Our length measurements were also accurate to 20mm each, so there is only one length stat put down in the table in order to save space.
Conclusion:
The final results show that osmosis stopped at between 0.25M and 1M. Again, though, both length and mass results tell us that osmosis stopped at two completely different places. So I would assume that this is supposed to happen, as it occurred both in our preliminary and final results. Whether this is because of our measurements (the fact we can't measure accurately beyond millimetres), I still don't know. We also see that as concentration of salt increased, osmosis decreased, and eventually worked so that water escaped the cells. That would be because as the salt concentration in the water increased, the water concentration decreased, until it got to a level which is below the water concentration in the cells, and osmosis always works from a high concentration to a low concentration, irrespective of where the low and high concentrations are situated.
The reason that the osmosis occurred into the plant cell before between 0.25 and 1M salt concentrations was because there was so little salt in the solution as a result of the low concentration of salt, that there was a high concentration of water, above the concentration of water in the cell. Again, osmosis always works from high to low concentration, so the water flowed into the plant.
The graphs show us that the change in the 'direction' of osmosis occurred quickly, then at a slower rate. This occurs in both our preliminary and final result graphs, so I would assume that this is meant to happen. This happens because as there is a large difference between the water concentrations in and out of the cell at 0.5M salt solution, that a lot of water flows between the membrane, causing a large change in mass/length. Then, because the difference between the water concentrations is less at 1.0M, less water flows between the membrane. This means, although the change in mass continues getting larger, the difference in the change in mass between 0M salt solution and 0.5M salt solution is much greater than the difference in the change of mass between 0.5M salt solution and 1.0M salt solution.
I can see 3 anomalous results in our experiment:
* 0.5M for mass (I don't expect such a large change in osmosis rates in such a little change in concentration)
* 1M for mass (I wouldn't believe the change of mass get more positive)
* 1M for length (I wouldn't believe the point of no osmosis to be over that range)
Evaluation:
My results supported my prediction, as I said when salt concentration increases, osmosis decreases, and eventually works in reverse, and that is what happened. I did say, though, that I would expect no osmosis to occur between 0.2M and 0.5M, but the actual range was a lot larger than that.
I also think that we need to collect a larger range of results, extending beyond 2M salt solution, because I believe that osmosis rates will actually rise back into positive increases in mass/length, because, as the theory section explains, salt levels do have some control over osmosis, so eventually the salt levels could get high enough to force osmosis to work the way it would in distilled water. But, as it is we collected enough results to disprove the hypothesis, and prove my prediction.
I am perfectly fine with the number of repeats we did, as our results seem to fit a common curve, and we only had a couple of anomalous results.
The way we worked the final experiment, I feel was very good. I feel we addressed most of the possible variables, and kept them as constant as we possibly could. But there are a couple of things I should comment on.
* Some of the chips were kept in their solutions for longer than the others, by even as much as 2 minutes. Although it doesn't seem a lot, it could have made the difference between the 1M solution's final length being 20mm, and it being 19mm, which would have made a lot more sense as a result.
* The measurements for length (mm), although very accurate in relation to using cm and m, were not accurate enough. It was incredibly hard to work out an average measurement, because we were not sure whether what we had measured was 19.4mm, or if it was 19.6mm. Again, it doesn't seem like a big difference, it could have meant the difference between the 1M solution's final length being 20mm, and it being 19mm, which would have made a lot more sense as a result.
* When we went to weigh the chips at then end, we noticed small amounts of water being deposited onto the scales. These droplets, though negligible in weight, were inconsistent, and so could have affected our results, although in a lesser way than the other two.
These problems, though apparent, I don't feel can have been helped, because they are such tiny problems, there do not appear to be effective fixes for them.
