The flaws for the preliminary experiment were that the temperature of the water was not the same and there was not enough in range of readings so one has to estimate what would have occurred between points. Another flaw is that there where a great range in shapes and sizes of the potatoes which would have changed the results. Another flaw is that we did not find any way in that which we could find that osmosis or plasmolysis could not occur any more then it is able to.
To tackle the above problems in the final experiment we shall do the following.
- Measure temperature of the water before the experiment so that it will make it a fair test without any change in temperature.
- Make a larger range in readings so it will be easier to compare results and it will be easier to draw a line of best fit as well as comparing the results to the prediction/hypothesis.
- We will use the same potato throughout the test so there will be no change in concentration gradient for all the potato cylinders.
- We will take down the mass once then 2 hours later to check that osmosis or plamolysis occurs any more.
Due to this above preliminary experiment and its results I have decided to draw up a prediction partly using the above results as well as using the scientific theory/knowledge. When writing up the prediction I have to take into account that the above results are not very accurate as I have acquainted with before and therefore may not always be a good source of scientific knowledge.
Prediction
With the potato in molar solutions of sucrose, there will be much change in the weight of the potato. This is because there is not much difference between the two substances. I believe that the weight and the size of the potato will not be altered much.
At the point of 0 molar sucrose solution there should be a significant change of mass because there is no sucrose solution on the outside and water should travel from the potato to the outside of the potato. I shall estimate there will be about a 50% increase. This is a very round figure and I may get results quite a bit under or over this figure.
The 0.2 molar sucrose solutions there will be a lot of change in mass and if the experiment if accurate enough then there will be about a third increase because the concentrations will be higher on the outside then the inside.
The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have a quite close concentration gradients, that is why I am predicting that the weight of the potato in this experiment should be increase by about, just less then a tenth or so.
The 0.6 molar solution of sucrose, I think, should make a little difference now, there should be little difference between the two concentration gradients and therefore the weight should decrease or increase, not noticeable for us to observate efficiently. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances. If this experiment was accurate enough then there will be no change in mass and there will be and equilibrium and there will be and isotonic region showing no change in mass if a graph is drawn to show this and where the line of best fit crosses the x axis then this is the molar solution it should not lose weight if used when done in experiment.
The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is tiny, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. As a result, I am sure that the weight of the potato will decrease largely from now on, because the potato tissues are surrounded by a stronger solution, it will probably become smaller, and shrink this process is known as plasmolysis. I predict this will probably lose about 5% of its weight.
My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.6 molar solutions of sucrose and greater.
Although these molar solutions I am not going to use exactly these molar solutions they will be a good use of referring and comparing to and a good bench mark as it is easier to predict these molar solutions than it is with the ones I am about to take on. It will be a lot harder for me to predict the ones I am about to take on because in the final experiment there is going to be a large range solutions therefore making it difficult to predict exactly. Although these are not all of the molar solutions they are the basic ones and will be used to compare.
Final tests
For these next three tests I am going to change as I have explained in all of the above bullet points to help ensure it is a fair and worthy test.
Obtaining evidence
After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes will not alter the weight of what it is supposed to be. I quickly took all of them out, and put them onto a piece of tissue paper, into their own groups.
When obtaining my results, I reset the balance, so that it would read zero with the small foam bowl on top of it. This was because, if I had weighed the potatoes with the bowl, then I would have to take the weight of the bowl away from that result.
Safety
As explained before safety is very important and the same procedures will be taken to avoid all injuries and hazards:
We will be using a very sharp knife, which could injure someone if it is not handled properly. And we will also be careful that the solutions do not get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us.
Another aspect of safety is that the cork borer can be used to an extent of harmfulness this is because when using it make sure that the potato is firmly on a surface if not the cork borer may go into ones hand and damage skin tissues.
But other than that, there were not any bigger matters to be cautious or concerned of.
Fair test
To make this a fair test the following will be applied:
Fair testing should play a big part in this experiment. If this experiment is not a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions.
First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible.
We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimetre, we will also be using a very sensitive balance so that we can get the best readings possible which is to the nearest 2 decimal places or to the hundredth of a gram.
But I believe one of the most important steps in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution.
To tackle this I found in my preliminary experiment that if you put the solution in first before the potato then the potato will float and will not be fully submerged. So we have decided to put the potatoes in first then the solutions. To avoid any confusion the test tubes will all be labelled first.
When using the balance, we will make sure that the balance is reading zero, before we put the 3 potatoes on it. This is so that we do not get a false reading, with the weight of our potato with the reading it had before which may lead us to the wrong conclusions. After the experiment, we will measure the 3 potatoes that should be dried as much as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
We will also be reading the measurements of the measuring cylinder by reading the bottom of the meniscus which will give us the most accurate results.
Carrying out the experiment in a constant throughout the experiment is important. To avoid temperature change, which might affect our 3 different sets of results, we will take the temperature of the solution into account.
Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the potato is put inside the test tube, and stop the clock as soon as 2 hours have passed.
Stopping the clock then taking them out and measuring them all in less than a minute is very much impossible because we lack the number of balances. Also there are obviously too many sets to go through at such a fast time. Therefore, we will try our best to weigh the potatoes as quickly and as safely as we can.
Getting and experimenting with the exact measurements of millilitres of sucrose solution and water is vital to this task. If the volume of one solution in a test tube is higher or lower than another, will affect the pattern of results later on.
In this experiment to make it a fair test we will take down the mass of the potato on the allocated time then we will put them back in the solution and weigh them again in 2 hours to check if it has done all the osmosis it can do if it has done all of the osmosis it possibly can then it will have no change in mass.
We will also make sure that the potato is fully covered by the 11 different kinds of solutions. This is because, is the potato is not covered up by the solutions, the effect of osmosis might not occur to the fullest.
Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well. To avoid such things as these one should carefully check all equipment
We will be using this range of solutions:
Method
- We will get the following equipment:
- Cutting tile – to cut the potato on
- Knife – to cut the potato
- 25 cm Measuring cylinder – to measure the solutions
- Distilled water – part of the experiment
- 1 molar sucrose solution – part of the experiment
- Potatoes – part of the experiment
- Tissue paper – to dry the potatoes after the osmosis takes place
- Balance – to weigh the potatoes
- Cork borer – to cut out potato cylinders
- Calliper – to measure the length and radius of each potato cylinder
- Tissues– to wipe off any excess water off of the potato cylinders.
-
Use the cork borer to bore the core of the large potato. You need a large potato because you will have to extract 11 potato samples. We will need 11 pieces so we have a larger range of results also giving more results.
- We will then make sure all the potatoes are dry on the outside of them because this will very much effect the results because the concentration gradient will be different and very much effect our conclusion.
- We will then measure each potato length using a calliper. To make this a fair test we will make sure the length of the potato cylinders are the same in length to the nearest millimetre. These will be 4 mm long it will depend on the size of the potato because we will need to use one potato only so they may be smaller or bigger than this.
- We will also need a calliper again to measure the surface are of the top of the cylinder to make sure they are roughly the same. We will ensure they are roughly the same to the nearest 10 mm squared. To find the area we will use the formula C= ∏ x D.
- Setup 11 test tubes and put the in a test tube rack to avoid any confusion put labels on how much sucrose and distilled water is going to be in there.
- Now we will take down the readings of mass of each potato cylinder we will do this to the nearest hundredth gram. After this is done then enter the potato cylinders into the allocated test tubes which will avoid any confusion in mixing up the test tubes.
- Before we add and solutions we shall use the tissues to wipe off any excess water which will make it a fair test and give us the accurate results that we want.
- We will then use the balance to take down the necessary readings. We will then put them back in the test tubes with the solutions in them and leave them for another 2 hours.
- We shall then use tissues to wipe off any excess water which will make it a fair test and give us the accurate results that we want.
- We will then take down the results again and if they have not changed mass since before then osmosis or plasmolysis cannot occur any more so they will not change mass again which makes this a fair test.
-
Work out the percentage change and draw tables and graphs to represent the data.
Tests
First test
These results show a strong pattern and therefore explain to me that the following experiment was carried out to an extent of sufficient accuracy and the test was conducted obeying the fair test guidelines.
The results show there is a strong negative correlation of values and will be recognised when plotted with a line of best fit.
At the point where there was eighteen ml of 1 molar sucrose solution and 12 ml of distilled water there was nearly a point of equilibrium. There was only a 0.02 grams of change which is the equivalent of 1.492537313% as you can see above in the table. This region is very close to the isotonic region and there is very little osmosis occurring which suggests that my prediction was very close.
I predicted that:
At 0.6 molar solution of sucrose there should make a little difference here, there should be little difference between the two concentration gradients and therefore the weight should decrease or increase, not noticeable for us to observate efficiently. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances.
Although here I predicted that there should be equilibrium at 0.6, and as I explained before it was going to be easier to base my hypothesis on these round figures, the solution 18 ml 1 molar sucrose and 12 ml water is the sucrose solution 0.6 molar so this will not be a problem here.
To work out what molar sucrose solution any of the above are, then you should divide the sucrose solution in ml by the total amount of solution which is 30 ml.
i.e.
To find out 27 ml sucrose and 3 ml water you should:
Divide 27 into 30:
27
----------- = 0.9 molar sucrose solution
30
This experiment shows that my hypothesis was very close to the actual experiment, this explains that the research conducted and the theory applied to my prediction was sufficient enough to predict accurately.
When the figures on the percentage column on the table start to go into minus figures the potato is now in the region where it is losing weight because it is doing the opposite of osmosis which is plasmolysis.
Graph to show first test.
As explained above the results resemble a strong negative correlation but now it can be seen very easily in the graph. This strong negative correlation is where the points are very close to the line of best fit and the negative part is the where the line of best fit goes down towards the x axis.
At the point where there is no sucrose solution and just thirty millilitres of distilled water you can see the potato has gained mass very significantly. The potato has increased by 42.10526316% which is just under a half of its original weight gained.
As you can imagine this potato was noticeably larger then before so we could clearly observate the change in mass by jus the difference in size.
In my hypothesis/prediction I predicted that:
At the point of 0 molar sucrose solution there should be a significant change of mass because there is no sucrose solution on the outside and water should travel from the potato to the outside of the potato. I shall estimate there will be about a 50% increase. This is a very round figure and I may get results quite a bit under or over this figure.
My test results show that my prediction was approximately right. This shows that the potato must have had quite a high amount of sucrose inside it because there was such a change in mass.
As we look more closely to the graph we see that there two points which are very close to the equilibrium. This explains that the increase in my range of solutions has helped in getting better and more accurate results. The two points which are close to equilibrium are, 18 ml sucrose + 12 ml water (0.6 molar) and 21 ml sucrose + 9 ml water (0.7 molar). As you can see there is only a 0.1 molar difference between the two solutions which explains the very little difference between the two points.
The interesting thing about these two results is that one is performing osmosis which is the 18 ml sucrose + 12 ml water (0.6 molar) and the one that is performing the plasmolysis is obviously 21 ml sucrose + 9 ml water (0.7 molar). This is because the isotonic region is obviously going to be very close to the regions where the potato is going to lose weight and where the potato is going to gain weight but in both cases the potato will have very little change in mass.
If you were to look at the graph more accurately at the point of which it crosses the x axis this is known as the isotonic region as I mentioned before. This point is around 20.5 ml of sucrose which roughly 0.16833’ molar sucrose solution which is very close to the other two pints but if the experiment was done with 20.5 ml sucrose and 9.5 ml water then it will eventually have no mass change.
Second test
These results again show a strong negative correlation, we can see this just because there is a pattern which is from a high positive number then it leads down to a negative number in the percentage change column, which is how we tell that it is a negative correlation.
Again in this table it is very much the same as the first experiment but there is not two points of near equilibrium this time there is only one.
Another issue of this table is that if you look at the weight before column all of the potatoes have nearly all the same weight which signifies that this test was conducted properly and to the full extent.
Graph to show test number two
As you can see on this scatter graph the hypothesis that the more sucrose solution outside of the potato leads to a decrease in mass, and the less sucrose solution outside of the potato leads to an increase in mass.
Here again the equilibrium is about 20.5 ml, so this potato contains more sucrose within it, and if there was a test at 20.5 ml of sucrose outside of the potato there would be no increase or decrease in mass, because the amount of sucrose outside and inside is the same. So this isotonic region is almost exactly the same as the test before.
In this graph you can see there is a strong correlation but there are a few points in which they are going away from the line of best fit. This point is where the is 15 ml of 1 molar sucrose solution + 15 ml of distilled water this is obviously the 0.5 molar solution.
At this point it turned slightly away from the line of best fit and if this line of best fit was correct the potato should have increased approximately 10%. Although I did not predict for a 0.5 molar sucrose solution I would have very much expected it to do so, it is not very reliable to always believe my line of best fit because this test was not totally fair and there were some non variables turned into variables by mistake.
When we look at the graph closely we can see that there are points in which sit on the line of best fit. These two points are:
- 9 ml sucrose solution + 21 ml distilled water (0.3 Molar)
And
- 24 ml sucrose solution + 6 ml distilled water (0.8 Molar)
These two points are likely to be the one of the most accurate in this particular graph because they are the only ones to hit the line of best fit exactly. Although one is performing osmosis and the other plasmolysis it does not matter.
Third test
The end result here is very much the same as the end results in the past two tests. The only small difference I can see is that the 30 ml sucrose solution + 0 ml water there is an extra increase in the percentage loss then the other two. This may have been because there was a slight alteration in one of the method points. In this test everything had to be done quickly to make it a fair test because of this some things may have been rushed a little. When making the solution the 30 ml sucrose solution + 0 ml water there is no need to put any water so it is even more rushed. This may have lead to an incident where extra sucrose solution has been add, which will of course make the potato lose extra weight but this may not be entirely true. It may also be because the potato cylinder was taken from a part of a potato that had very little sucrose making it transport more water. But this again may not be entirely true.
Graph to show results on third test
This test is a lot easier to analyse then when on a table but rather on a graph. Straight away we can see that the x intercept point or the isotonic region is different to the other two past tests. Here the equilibrium is at the point where there is 20 ml of 1 molar sucrose solution and 10 ml of distilled water this is a 0.333’ molar sucrose solution.
This basically may be the fact that this potato was different to the others and probably could not be avoided.
In this test there is only one point which hits the line of best fit perfectly and this is the solution:
- 21 ml sucrose solution + 9 ml distilled water (0.7 Molar)
In this test there is one significant anomylous result and that is :
- 0 ml sucrose molar solution and 30 ml distilled water
This have been again because of the fact that the potati was not the same all the way around its surface.
Evaulation.
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. I think I took easily enough results for the amount of concentrations that I was using. But if I took even more the test would be an even more of a success.
The time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the potato cylinders.
The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. This way would have allowed me to also find out the isotonic point far more accurately then the ones I estimated in the past experiments..
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. Even though I did measure the surface area it sill would not be fair because they still were not the same size.
As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a burette which would be a lot more accurate and leave less room for human mistakes. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each potato cylinder on a more accurate scale, e.g. not to 0.00g but to 0.0000g.
There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by human error.
When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated
I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
To extend the research and the amount of knowledge of this experiment I could use different potatoes like sweet potato because obviously they will have different concentration amounts inside.
I could extend this even more because I could use different tissues instead of potatoes. This will make a lot of difference because it will extend my knowledge from osmosis in a potato into osmosis in an organism/ plant.
By Abdelaziz Marzoug Osmosis Coursework 10 E
