Top-Pan balance-to weigh the potato cores.
Two potatoes to provide the potato cores, five different concentrations of sucrose solution; 0.2M, 0.4M, 0.6M, 0.8M and 1.0M. (0.0M is just dilute water). Distilled water-to make the different concentrations. .
Labels for the test tubes(18 labels)-labelling each test tube would prevent any confusion in which concentration each test tube is and which test tubes are mine.
Test tube rack for each molarity level(5 test tube racks)-This is to avoid any confusion about which test tube is which concentration of sugar solution so therefore I will not get the wrong results.
Cutting Tile-To cut the potatoes on.-This will prevent and other substances touching the potato cores.
25cm3 measuring cylinders-to measure the sugar solution .
Ruler-to measure the potato cores accurately.
Size 6 cork borer-to take the potatoes out of the potato easily.
Hypothesis
Osmosis is the net movement of water molecules from a high concentration to a low concentration through a partially permeable membrane. The reason why osmosis occurs through a partially permeable membrane is to only allow small molecules to pass through but not the large molecules. Therefore, the tiny holes in the membrane allow the small water molecules to pass through, but the large solute molecules are too big to pass through the partially permeable membrane. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium,(unless there is a factor which affects the potato core reaching this point, for example, the potato core has not been left for long enough or the overall conditions (temperature) aren’t right) where the concentration of water inside and outside the potato cells are equal (isotonic).However, some potato cores may not necessarily reach a state of equilibrium; it might take longer than the time I plan to leave the potato cores, and I have to appreciate this factor. At this point, there will be no change in the length, volume and mass of the potato cores as the net movement of water will be zero, no net osmosis has occurred. A solution has two parts to it, the solute and the solvent. The solute dissolves in the solvent. An example of a solute is sugar and an example of a solvent is water. A concentrated solution has a lot of solute dissolved in the solvent. A dilute solution is where only a small amount of solute is dissolved in the solvent.
Further Information On Potato Cells
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant sells become ‘turgid’ when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant ‘stand up’ into the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become ‘flaccid’. This is the exact opposite of ‘turgid’ The contents of the potato cells shrinks and pulls away form the cell wall. These cells are said to be plasmolysed. When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity, We call this incipient plasmolysis. ‘Incipient’ means ‘about to be’.
Prediction
I think that when the concentration is changed, the mass will also change. When the solute outside the potato is higher than the concentration in the potato, the mass of the potato core will decrease. When the solute outside the potato is lower than the concentration in the potato core, the mass of the potato will increase. However, the only time the mass will not change is when the concentration of the water is the same in and outside of the potato core. I think that the potato core will lose most water when there is a higher concentration of sugar solution and will gain more water when there is a lower concentration of sugar solution. The diagram below helps explain my prediction as well.
When the two solutions are divided by a semi permeable membrane the water will move from the area of high concentration to an area of low concentration until both sides are equal (have reached a state of equilibrium) unless there is insufficient time.
Range and Numbers
There will be six different molarity levels; 0M, 0.2M, 0.4M, 0.6M, 0.8M and 1.0M. I will have three potato cores for each molarity level and I will take the average to give me more accurate results and reduce the amount of anomalous results.
Preliminary Work
This will be done before the main experiment mainly to see how long I should leave the potato cores for osmosis to occur. I will do two separate experiments to conclude what will be the best durati
2nd Experiment
Time left: 20hours 34mins
CONCENTARTION INITIAL MASS(g) FINAL MASS(g) CHANGE OF SUGAR SOLUTION IN MASS
0M 3.41g 4.11g +.7g
0.5M 3.34g 2.95g -.39g
1M 3.41g 2.95g -1.22g
Conclusions From the Preliminary Results
n of time to leave the potato cores. Three test tubes will be filled with 20ml of different concentrations; 0M, 0.5M and 1.0M. The reason I will use these specific concentrations for the preliminary experiment is to find out what will happen to a potato core where it is put in a concentration of under 0.5 M and above 0.5M.
The three test tubes will be labelled with their molarity level on the test tube so I know which test tube will have which concentration. The potato cores will be taken out from the original whole potato using a cork borer. They will be then cut to the same size (4cm) as accurate as possible.
They will then be wiped with tissue paper before weighing them to get rid of any excess liquid which might come from after the potato core is taken out of the test tube which could add to the mass of the potato cores, which would give inaccurate results.
A petri dish will be placed on to of the top-pan balance to weigh the mass of each potato core. The mass of each potato core will be recorded and then put in each of the three concentrations.
In the preliminary experiment, I have only used one potato core for each concentration seeing that I am short of time.
Preliminary Results
First Experiment
Time left: 1hour 7mins
CONCENTARTION INITIAL MASS(g) FINAL MASS(g) CHANGE IN MASS
OF SUGAR SOLUTION
OM 3.44g 3.81g +.37g
0.5M 3.41g 3.16g -.25g
1M 3.43g 2.81g -.62g
2nd Experiment
Time left: 20hours 34mins
CONCENTARTION INITIAL MASS(g) FINAL MASS(g) CHANGE OF SUGAR SOLUTION IN MASS
0M 3.41g 4.11g +.7g
0.5M 3.34g 2.95g -.39g
1M 3.41g 2.95g -1.22g
Conclusions From the Preliminary Experiment
I have discovered what safety measures need to be taken into account when doing the main experiment.
Safety
a)Safety glasses are not a vital part of safety, since there aren’t any harmful chemicals I will be using in this particular experiment.
b) All apparatus should be labelled clearly, so that there would not be nay confusion, which could cause accidents.
c) A first aid kit should be kept close by to save time in case of a cut or a graze should occur during the experiment. A cut or a graze can be avoided by being very careful with the apparatus in the first place.
I have also found that some apparatus are better to use than others:
a) I have discovered that I got a more accurate length of the potato core using a scalpel rather than a safety razor or a knife. The reason being that it was easy to handle and I could control it in a safe manner.
b)Tissue paper was used rather than any other material to soak up the excess water on the outside of the potato core. This is because it is the only material which is only absorbent enough to soak up the liquid from the outside of the potato and not the inside of the potato core, unlike the ‘J’ cloth.
c)When taking the potato cores out of the potato, I discovered it was easier to get the cores out if the cork borer was used horizontally to the potato. In addition if the potato cores were taken out like this the potato cores would come out in perfect cylinders.
Main Experiment
I will have three potato cores for each concentration, and they will all be in separate test tubes, not all three in one test tube. I have decided that I will leave the potato cores in the solutions for 24 hours. This length of time is suitable because I will do the experiment in the morning and come back next morning to analyse the results.
This table shows how the concentrations were mixed.
Volume of Distilled water Volume of 1Molar Sugar Concentration of
(cm3) Solution (cm3) solution(M)
20 0 0.0
16 4 0.2
12 8 0.4
8 12 0.6
4 16 0.8
0 20 1.0
Results of the main experiment.
A Table To Show The Mass Of A Potato After It Has Been Put In A Given Sugar Solution.
Concentration of the Test Tube Initial Mass Final mass Percentage change
Sugar solution (M) of potato (g) of potato(g) in mass
0.0 1 3.43 3.85 12.24
2 3.44 3.87 12.5
3 3.46 3.86 11.56
0.2 1 3.33 3.51 5.41
2 3.36 3.55 5.65
3 3.39 3.61 6.49
0.4 1 3.35 3.10 -7.46
2 3.43 3.12 -9.04
3 3.37 3.20 -5.04
0.6 1 3.40 3.04 -10.59
2 3.35 2.98 -11.04
3 3.49 3.09 -11.46
0.8 1 3.40 2.90 -14.71
2 3.45 2.93 -15.07
3 3.41 2.91 -14.66
1.0 1 3.42 2.90 -15.20
2 3.46 2.92 -15.61
3 3.45 2.93 -15.07
(I have worked out the percentage change in mass for each test tube above as follows: % change=change/original weight x 100) (I have worked out the average percentage change in mass for all three test tubes below as follows: add all the averages and divide them by 100)
Concentration of Sugar Solution(M) Average percentage change in mass(%)
0.0 12.1
0.2 5.85
0.4 .18
0.6 -11.03
0.8 -14.81
1.0 15.29
Analysis
As the concentration increases from 0.0M when it gained a lot of water the amount of water started to decrease as the concentration was increasing.
The two points above the X-axis are positive and the four points below the X-axis are negative. The two positive points indicate an increase in mass and the four points below the X-axis indicate a decrease in mass. There is one anomalous results, which is at the point 0.2M, most likely due to a human error.
The graph shown in the previous page gives the curve between points for the percentage change in mass of the potato cores. The graph is a curve sloping downwards and it does not intercept the origin, therefore, concluding that the percentage gain and loss in mass and concentration are not directly proportional.
I have noticed that as the concentration of the solution increases, from 0.4M and above, the percentage change in mass decreases. The graph shows that the percentage gain and loss is inversely proportional to the concentration. The gradient changes in my graph. It gets less steep (from values 0.4 to 1.0M) as the concentration of sugar solution increases. The reason for this is because the potato core is becoming as flaccid (limp, meaning that the cell structure…….) as possible and so the change in mass of each molar concentration is becoming closer and closer. From the line of best fit that has been added in, it can be seen that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable.
The graph shows that the potato cells increase in mass in solutions with a higher water concentration and decrease in mass in solutions with a low water concentration. When the concentration is 0.8M and 1.0M, there appears to be little water loss ( there is only a .48% difference), suggesting that the cell is close to being fully plasmolysed. Below is a diagram of a plasmolysed cell. (what does it mean where your line crosses the x axis? Need to comment about opposite ends of graph as well.)
The prediction I made is supported by the evidence obtained from this investigation. I predicted that the potato cells would increase in mass in a high water concentration and decrease in mass in a solution with a lower water concentration, which I now know is true.
Evaluation
I feel that the experiment on osmosis has been very successful seeing that I obtained accurate results from which I was able to draw a good graph. I feel that I had obtained enough results to draw an informative graph, and the time that I had left the potato cores in the different concentrations of sugar solution, which was 24 hours, was enough for sufficient osmosis to occur. However, if I were to repeat the experiment to improve it, I would leave the potato cores in the sugar solution for an even longer period of time to allow more osmosis to occur and I could possibly find the actual saturation point of the potatoes cores rather than something close to it.
The range of the different concentrations of sugar solutions was were suitable for the experiment but if I were to repeat the experiment, I would create more concentrations to give me more varied results, i.e. more than one Molar. So I could maybe use 1.5M, 2M, 2.5M, 3M etc. This would allow me to find a definite or more accurate isotonic point. I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. I could have possibly use a syringe instead of relying on the human eye. This would ensure that I have an accurate amount of sugar solution in each test tube (20ml in each test tube). I could have weighed each potato core on an even more accurate top-pan balance (e.g. 0.0000g instead of 0.00g).
All my points on the graph were accurate apart from one anomalous result at 0.2M. This is most likely due to human error. However, I can still make a firm conclusion due to the fact that all my other points in the graph are accurate and reliable.
When the potato cores were removed from the sugar solution and dried, the tissue paper might have dried some of the potato cores more thoroughly than others so therefore, some would have more water stored than others, which would add to the mass of the potato core. If I were to repeat the experiment I would ensure that all the potato cores were dried in the same way and for the same amount of time.
I did not take into account the effect of fluctuations in the room temperature on my experiment, although I couldn’t have controlled the temperature inside the laboratory, I could have covered each test tube with cling-film to prevent any solutions escaping through evaporation.
I was forced to rely on imprecise tools to cut the potato cores such as rulers, scalpels and my own judgement. I was able to partially solve the problem of different size potato cores by calculating the percentage change in mass as opposed to the actual change. I calculated the percentage change in mass by dividing the change in mass by the original mass of the potato core and then multiplying it by one hundred. I got the final percentage change in mass by calculating the average of the three different percentage change in mass.
Some potato cores were still in their test tubes while I dried and weighed the others. The way I could solve this is to empty all the potato cores out of the test tubes, then dry and weigh them.
There are a number of different ways to expanding my experiment. I can could introduce other variables such as the temperature; would osmosis slow down or speed up or will osmosis even occur in a low temperature, such as in a fridge? The size of the potato cores can effect the rate of osmosis. Would the lower surface area to volume ratio of a smaller potato core affect the speed off osmosis and would a potato core cut in tow halves react differently compared to a regular potato core? I can also compare the results yielded by two potato cores in separate test tubes and two potato cores in the same test tube but in the same concentration of sugar solution. I could also t likely to be different. I could investigate whether or not different varieties of potatoes yield different results and trends. Similar vegetables can be used such as onions, celery and many more.