But what exactly is Osmosis?
Each cell is surrounded by a membrane, which has tiny holes in it. This membrane is partially permeable (just like the visking tubing) It allows small molecules to pass though but not larger molecules.
Osmosis is the movement of water for ma high concentration (or weak solution, on this case 1 molar water) to an area of low concentration (a strong solution, in this case 1 molar of sugar solution) through a partially preamble membrane. So, the water is moving both ways to even up the concentration. if there is more movement one way, it is said there is a net movement of water into the area where there is less water.
An example of osmosis in Animal Cells
Animal cells have no cell wall to stop them swelling. So if they are placed in pure water, they take in water by osmosis until they burst.
Red blood cells when placed and burst
in water the
cell swells up
This information helps to me find out and predict what will happen to my potato chips. This information shows me that the potato chips when in a sugar solution will loose weight because water will diffuse out to balance concentration. However when the potato chips are water the potato chips will increase in mass because the water will diffuse in to balance the concentration.
Apparatus:
Cork Borer
Water
Forceps
Measuring Cylinder
Tile
Knife
Potato
Digital Weighing Balance
6 Test Tube
Test Tube Rack
Paper Towels
6 Sticky Labels
Pipette
Cling Film
Sugar Solution
Fair Test
In the experiment of osmosis the should only be two changes
- The different molarities of the sugar solution
- The change in Mass of the potato chips
To keep these two things the only changes in my experiment, I will make sure that the potato samples ate the same measurement being at 2cm. They must be at the same measurement because if one is long than the other it will have a larger surface area therefore having a quicker rate of osmosis. I will also use the same potato for each chi, this is because if the age of each chip was different one chip would contain more water than the other making the rate of osmosis differ and not providing a fair test. I will also make sure that evaporation does not take place in the experiment this is because if the sugar solution evaporates pass the level of the potato it will have less surface area making the rate of osmosis slower. So to avoid this cling film will be placed on the mouth of the test tube. I will also ensure that there will be accurate sugar solution in each test tube to make sure this is possible I will use a measuring cylinder and pipette will be washed each time it is used otherwise there could be a possibility of the test tube being contaminated with a different morality.
To make sure the experiment is accurate an average will be taken of the six sets of results. The temperature may affect the reality of this experiment so I will make sure that the experiment will be kept in a cool and dry place. Also three chips will be placed into the test tube to obtain a average to make sure the test is fair and a more accurate graph.
Safety:
This experiment seems to be quite harmless, nevertheless I will take into consideration that the knife that will be used may be sharp and can cause injury. I will also be careful the solution should not get into the body internally, and also I will be wearing an apron so to protect my clothes and I shall also wear goggles to avoid the solution to come into contact with my eyes.
Diagram:
Here is a diagram showing the apparatus, and how the experiment is set up:
Procedure:
I plan to carry out this experiment by using all the safety issues and fair testing to give me the most reliable and most accurate set of results.
1. Collect apparatus as shown above in diagram.
Take one large potatoes and check that they are both healthy and hard.
2. Using a knife peel the potato.
3. Using a scalpel and ruler cut the potato into cylinder shaped chips, which are 5 cm long. Be very careful whilst cutting the potato, as the scalpel is exceptionally sharp. Cut 18 chips like this.
4. Take a test tube rack and place 6 test tubes and using the sticky labels labelling them 0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1 molar, this is so that we know which test tube contains what amount of sugar solution.
5. Using a measuring cylinder measure out different amounts of the sugar solution being at 0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1 molar, and also distilled water which is then poured into the test tubes in a percentage ratio giving me the various molar concentrations.
6. Then weigh every potato chip on an electronic balance and recorded the weights.
Weigh each chip 3 times to make sure the test is fair.
7. Swiftly put three potato chips into each test tube.
8. Leave experiment in cool dry place over night.
9. After a night drain out the solutions in the sink and place all the chips on the paper towel.
Place chips in the order in which they were placed into the test tube so as not to confuse as to which chip came from which solution.
10. Then dry each chip with the paper towel and then place each one on the scales so that they can be weighed.
11. Measure each potato chip accurately on the electronic scales and then record the weights.
This is the molar concentration that will be used:
Results
This results table shows the weight of the potato chips before they were placed into the sugar and water solutions and the average of all the potato chips in grams.
This is the result of the weighing of the potato chips after the experiment has been left over night. It will show if osmosis has taken place.
There is a graph attached that shows my results.
Here is what I plotted on my graph.
Analysis
The evidence I have obtained form this experiment support the prediction I have made. It also shows that the potato cells increase in mass in solutions with a high concentration of water, and decrease decreases in mass in a solution with a low concentration of water. If the concentration of a solution into which a potato chip of 2cm of a potato is placed is greater than a certain level the potato chip will contract, and if the concentration is less than that level it will expand. This can be seen in living cells.
The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high concentration of water), water will move across the semi-permeable membrane into the cell (lower concentration of water) by osmosis, making the cell swell. This cell is now turgid. If this were done with potato cells the cells would increase in mass because of the extra water. If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.
The greater the concentration of water on the out side of the cell the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water out side the cell the greater the amount of water that leaves the cell.
In this experiment I believe I collect enough data to support my hypothesis. The experiment has a yielded graph, which proves my point noted in the prediction. The gradient of the graph decreases steeply and the potato looses mass.
Evaluation
The experiment was very successful in my opinion. I obtained a 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 which was;
0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1 molar. The time that I used for the experiment was 24 hours (over night) was enough time 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 chips. I could also possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.1m, 0.2m, 0.3m and so on.
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 also 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 also dimensions. 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. This would ensure that I have an accurate amount of solution in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g.
There were not any anonymous results, but some were not as close to the line of best fit as others. This could be because 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. 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.