Variables
To ensure my experiment was a fair test I had to keep some variables in my experiment the same whilst changing only one key variable. The variables that I could have changed were the temperature during the experiment, the environmental conditions during the experiment, the length and width of the potato chips, the volume and strength of the solutions, how the potato chips are weighed and lastly how long the samples submerged in the solution.
I will carry out all of my tests at room temperature which will control the factor of temperature. To ensure that environmental factors like light and humidity do not affect my results all of my samples will be placed in the same conditions in the same place. I will use the same weighing scales on each of the chips to remove the possibility that each set of scales take a different reading. All of my samples will each have the same surface area, I will do this by cutting each potato chip using the same apple corer (controlling the width) and then cutting the end off of them all (controlling the length). This will result in each of the samples having a very similar surface area and volume. The outer skin of a potato has different cells from those inside the potato and to stop this from affecting my results I will cut the ends off of all of my samples.
Apparatus
- Table Knife
- Cutting tile
- Scales
- Potato
- Measuring Cylinder
- Beaker
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1,2,3,4 and 5 moldm-3 salt solutions
- Pure water
- Apple corer
- Baby Wipes
- Goggles
- Stopwatch
Test Stages
- Pick three average sized ground potatoes and check that they are hard and healthy.
- Use the same apple corer on each potato to cut 15 individual potato chips.
- Use a table knife to cut the end off of each chip and make them all approximately 5cm long on a cutting tile.
- Weigh each of the potato chips individually on an electronic balance and record their weight.
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Take 18 beakers put them into groups of three, label each group: water, 1,2,3,4,5 moldm-3.
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Measure out 120ml of water, 1,2,3,4,5 moldm-3.
- Pour 40ml of solution into each beaker of each group.
- Place 1 potato chip into each beaker making sure they are all fully submerged, then start the stopwatch.
- Make a note of which chip went into which beaker.
- Leave the beakers at room temperature for exactly 72 hours.
- Remove the potato chips from the beakers and place each chip onto a sheet of kitchen roll
- Leave the chips to dry for 3 minutes at room temperature.
- Measure each potato chips mass using the electronic scales and observe any other details.
Prediction
My hypothesis is that the potato chips that are left in the most concentrated salt solutions will decrease in mass the most. I also think that the potato chips that are left in the solution of pure water will increase in size dramatically. I say this taking in factors such as osmotic pressure and osmosis itself.
Preliminary experiment
Before I started my final test I decided to do a preliminary test to ensure that there was a measurable effect and there was therefore something to observe. I place a peeled potato chip into a beaker of 5 moldm-3 salt solution. I then left it for 24 hours and I weighed the chip before and after my short test. I found out that osmosis had indeed taken place and I should then continue with my final experiment as planned.
Results
Analysis
The potato chips that were left in pure water gained an average percentage change in mass of +24.6. This is because the chips were less concentrated than the pure water that they were left in, the water molecules therefore filled up the potatoes’ cells and so added mass to the potatoes themselves.
The potato chips that were left in the most concentrated salt solutions got lighter by an average percentage mass change of -31.6. This is because the potatoes’ cells were more concentrated than the solution that they were left in. The water molecules that were in the potatoes’ cells therefore diffused through the semi-permeable membrane into the salt solutions.
The samples that were left in the 3 and 4 moldm-3 salt solutions only had an average percentage mass change of +2.42 and -1.91 respectively, this was because the difference in concentrations between the solutions and samples were very small. Osmosis could only therefore diffuse very few water molecules through the semi-permeable membrane, resulting in a very small delta mass change.
The samples that were left in 1 and 2 moldm-3 salt solutions had a average percentage mass change of +11.2 and +7.86 respectively. The potato chips had a lower concentration than the salt solution that they were placed in. The water molecules therefore diffused through the semi-permeable cell membrane of the potato chip and into the potatoes’ cells. This meant that they both gained in mass and became turgid.
The graph was practically a straight line and shows that the stronger the salt solution the greater the loss in mass.
From the results that I have collected I can tell roughly what the concentration of water inside the potatoes’ cells is. The water concentration inside the potatoes’ cells must be between 3 and 4 moldm-3 salt solution because that is when the percentage mass change changes from positive to negative. Meaning the water concentration must be between those two salt solutions.
Evaluation
Results
I am very pleased with how the experiment went and in my opinion it was very successful. The results that I have collected support the prediction that I made earlier in my coursework. The samples that were left in pure water gained the greatest mass and the samples that were left in the strongest salt solution lost the most in mass.
Based on the data that I collected I do not think that I have any anomalous results. All of my results were very close to each other but some were not as close to the line of best fit as others. This may have been caused by human error but I do not think that they can be considered anomalous.
I think that the results that I collected were reliable and as accurate as I expected. I collected a lot of results to ensure that any anomalous results/outliers could be discarded.
Method
What could have gone wrong?
The experiment that I carried out was simple but lots of there was not much room for human error. There were lots of things that could have gone wrong due to human error or the lack of advanced, specialised equipment. When the potato chips were removed from the beakers some of them might have been left to drip for longer periods of time than others, this would have made it and unfair test and would have added mass to some of my samples. If I was going to do this test again then I would try to ensure that all of the samples were dried in the same way and for the same period of time.
Another part of my experiment that could have caused error was if excess liquid was left on the weighing scales after weighing each potato chip. To overcome this I wiped off the scales after each time I used it using a baby wipe, if I had not done this then extra liquid would have been added to each sample. This would have caused it to become an unfair teat and for my results to be useless.
It was also difficult to cut the potato chips accurately. I tried very hard to make the ends of each of my samples the same to ensure all of them had the same surface area. If I was to do my test again then I would have used a machine to cut the potato chips. This would provide me with more accurate data.
How to improve my experiment
If I was to do this experiment again then I would have used more advanced, specialised equipment. I would mainly try to improve how I measured the solutions and how I cut the potatoes. I might also have carried out more tests on each solution to get more accurate data. If I wanted to explore osmosis further then I would do the experiment using more moldm-3’s, instead of using 1,2,3,4,5 I would go up in 0.5’s. e.g. 1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0. This would also help to investigate the concentration of the potatoes’. The weighing of the potatoes was another area in which I think that I could have improved my experiment, the scales that I used were only 0.00g but I would have used 0.0000g if I had had the opportunity. All of this would improve the data that I could analyse and would provide me with a more accurate graph with which to use.
Safety Precautions
The experiment that I did was not a very dangerous one, but I still had to consider some safety precautions. I wore Goggles during the whole of my test in case any liquid was released from any of my samples, this was of utmost importance when I was using the apple corer to cut the potato. This presented another hazard. Whilst cutting the potatoes using the apple corer I had to be extra careful not to exert too much pressure and I had to keep my fingers well out of the way. These were the only real safety precautions that I had to take because it was a relatively safe experiment to perform.
