The diagram shows how pressure is built up in osmosis
This diagram shows what I will be doing during this investigation
Prediction
My predications for this investigation are:
- As the concentration of the sodium chloride solution increases, the mass of the potato chip will decrease, this is because the solution outside the chip is more concentrated, therefore the chip will need to give out more water, to try and balance out the solution outside as a result of this the chip will lose mass.
- If however the sodium chloride solution which the potato chip is placed into, is less concentrated than the solution within the chip, than more water will pass into the potato chip. This is because the outside solution is trying to balance the solution within the chip, so as a result the chips will gain weight.
Apparatus
- Test tubes
- Beakers
- Potato core
- 2M salt solution
- Mechanical weighing scale
- Filter paper
- Stop watch
- Distilled water
- Petri dishes
Fair test
In order to make this investigation a fair test, the entire variable must be controlled.
- I will be using the same potato in each investigation and more importantly, the potato I will use will be raw at all times as a boiled potato can affect my end results.
- I need to keep the volume of sodium chloride solution the same in each test tube.
- The length and the area of each potato chip have to be the same so the surface area of the potato will be constant.
- The temperature will also have to constant as it could affect the rate of osmosis.
- The concentration of the salt solution will have more effect on the chip than based on how long the chip has been left in the solution. When equilibrium occurs no more osmosis occurs, this will still stay the same even if the chip is left in the solution for a longer period of time. Increasing the concentration will decrease the amount of time taken for equilibrium to occur.
Method
The apparatus that I will be using must be chosen carefully so that I will have more accurate results to reflect upon.
I will have to follow these steps in order to carry out the investigation.
- Cut the potato using a potato corer into equal pieces
- Cut the sore down in the middle
- Dry the core using filter paper
- Weigh the sore on the electrical weighing machine
- Using your beaker, place a sufficient amount of salt solution into it and then pour a sufficient amount of salt solution into a test tube
- Put the core into the test tube and immediately start the stop watch
- Mark out the different concentration on the test tubes
- The constant time that I will use is 10 minutes. When the 10 minutes are up I will remove the chip and dry it thoroughly as I do not want excessive mass
- I will then make the solution. In order for me to make the solution I will need to first find out what is the highest morality I am going to be using. In this case it will be 2m. I also need to find out what is the maximum amount of solution I will be putting in each beaker; in this case it is 30 ml. Using this I can work out how much water and salt solution should go into each beaker. I have to first divide the maximum amount of solution I will be using by the maximum amount of morality- so it will be 30ml divided by 2m. After doing this I have to then multiply it by the morality I need to get, so I find out how much slat solution I need to put in- 30ml divided by 2m = 15ml.
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- 15ml * 1.5m (the morality I want) to get 22 ml of salt solution. Now that I know how much salt solution to put in I need to put in water to makes sure that there is exactly 30 ml of solution in each beaker.
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Then after 24 hours I will take them out, rinse them on filter paper and reweigh them.
- I will repeat this experiment using different solutions and concentrations
Safety
To make sure that the experiment is safe I need to make sure that I am wearing goggles throughout the investigation. Furthermore, I will not be leaving any equipment on the table alone as anything could happen. If left on the table without supervision, there could be a spill or even shattering which could lead to one of my friends being injured. I will be not throwing any thing around and just make sure am careful not to spill any solution or water on the floor.
Preliminary experiment results
I have done a preliminary experiment to make sure if what I was doing was correct and any improvements that I could have make for my real experiment. These are the findings of my experiment. I did this experiment in two different solutions, one on 2 m solution and one in 1m solution.
I didn’t get to record this experiment because I forgot to record the weight of the chip after the experiment.
To work out the percentage change I will need to use the following formula
Percentage change= Change in mass x 100
Mass before
Observation
I carried out this experiment three times to get and average, so I can get accurate results for my experiment, I made up 3 sets of 6 solutions, 2m, 1.5m, 1m, 0.5m, 0.1m and pure water. With these results Ifound out the average of the result. To get the average result I added the mass changes together and the divided by three, because I made three sets of results. We also made a percentage change in the mass, to show us how much mass is being lost as the molality increase. To find the percentage change, we divided the mass change by the 1st mass, then multiplied it by 100.
To work out the percentage I used:
Percentage change= Change in mass x 100
Mass before
From the results above I can conclude that, as the concentration of the solution doubles, the mass loss also doubles. From the average results I can see that the mass decrease as the solution morality increases. I can also see that the point of equilibrium happened at about when the solution was of 0.5m. The reason for this is that, at this point there were almost 0.0 changes in the mass; this meant that there is an equal amount of water molecules on either side of the semi-permeable membrane.
Analysing evidence and drawing conclusions
I have made four graphs each for a different experiment I did to conclude my findings. I did three experiments, which then I could use to get me and average results table and also made my results more accurate to reflect upon.
The graphs I have drawn up show that osmosis was working efficiently, because you would expect the longer the chip stayed in the solution the more mass it will loss, and that is what my graph shows. It also shows that as you increase the mortality then the mass change will also increase, this is said to be directly proportional, when one increases so does the other. Furthermore, my graphs show that there is a strong and positive correlation between the ‘percentage change in mass’ and the morality of the solution’, as the points were close together. The pattern in my graphs show that as the morality increases, the mass change will also increase as well.
I found out that as the morality increased the more mass was then lost within the potato chip. This is due to the fact that the process of osmosis is occurring. During the period of time, the water particles in the chip were being transferred into the outside, this shows the way that mass is lost. On the other hand, more concentrated solutions would balance each other out and equilibrium is established. At the start of this experiment, the plant cells were very firm and strong because of the cell wall. As osmosis occurred, the cells became more and more weak and firm and soon died, this was due to the cell walls getting weaker and weaker. As you can see in my graphs, that osmosis was still occurring even after the morality of the solution increased.
After the vacuole shrunk and the cells died the chip also died, so no more osmosis could occur, as there was no more water particles left inside the chip had to balance out the solution that was outside.
Furthermore, the results that I had recorded show that my predictions at the start of this investigation were correct. The predictions that I had made at the start of this investigation were correct and matched my findings and results.
Evaluation
The experiment I did was and wasn’t that much of a fair test. I say this because in some place like the size and the weight of the potato wasn’t constant. Some of the chips had bit of difference between them some of the potato chips were smaller and lighter than others. The other parts of the experiments was fair we carried out the experiment properly and made sure that there was the same amount of sodium chloride surrounding each set of chips.
To make our measurements as accurate as possible I used the same dimension cork borer and a 15 cm ruler to measure out the potato chips as accurate as possible, even though there were some slight difference, they didn’t make much of a difference to outcome of my experiment. I used measuring cylinders to help measure out rights amounts of salt solution and pure water. When the measurements got a bit tricky, that is to say we had to measure out 1.5ml, we used a smaller cylinder, ones were it goes only up to five centimetres of volume. There were some problems that encountered me when measuring accurately mainly due to the confusion between certain apparatus and their properties, however, these problems were overcome instantly once realized. The pattern I expected, was that as the molality increased than the mass loss will also increase, I saw that this pattern was followed by the experiment, because as we measured the different chips in different solution, after the experiment, the chips in the more concentrated solution lost quiet a lot of weight, whereas the chips in the lower concentration gained weight. I have shown this in my graphs and my results tables. I think that my results are reliable because the points on the graph is a straight line so my results must be accurate.
If I done this experiment again I would improve it by making sure that the potato chips are the same length. Another way in which I could improve is that I need to be quicker in measuring and placing the chips into the solution, I say this because, the chips I put in first have had a longer time to go through the process of osmosis, and the chips I weigh after the first ones have an unfair advantage as, as they have had longer time for osmosis. So I need more than one person measuring and placing the chips in the solution, so we don’t tamper with the results.
