Variables
- Temperature
- Volume of sugar solution
- Concentration
- Weight of potato
- Surface area
I have chosen to change the concentration because I hope this will give me a good varied set of results to work with. The concentration will be measured in molars.
To make sure this is a fair test I will have to keep all the variables constant apart from the concentration. If I did change one of these variables, for example, if one potato chip were 1cm longer than the other there would be more space for osmoses to occur, therefore the test would not be fair.
To make sure the test remains fair I will do all my experiments at room temperature, use the same type of potato, which will be kept at the same size and weight and have been treated in the same way. I will also use the same volume of the solution in the test tube is kept fair. I will use an accurate electronic balance, showing grams to 2dp in this experiment, to ensure even small changes in mass are recorded. I will also keep using this balance throughout the experiment so measurements do not vary due to any change that may be introduced by different scales. The water particles pass from a high concentration to a low concentration. I predict that the lower the concentration of the sugar solution in the test tube the larger the mass of potato will be. So in a high sugar concentration the potato will have a smaller mass.
This is what I think my graph will look like.
I will use a range of the sugar solutions from 0 molar to 10 molar in 2 molar steps. This should give me a good range of results to look at.
Hypothesis
I predict that the higher the concentration of the sugar, the lower the mass of the potato at the end of the experiment. This is because with a higher concentration of sugar in the water, there will be less water molecules in the solution, so it’ll take less time for them to diffuse into the potato.
Water Potential
The water potential of a solution is a measure of whether it is likely to lose or gain water molecules from another solution. A dilute solution, with its high proportion of free water molecules, is said to have a higher water potential than a concentrated solution, because water will flow from the dilute to the concentrated solution (from a high potential to a low potential).Pure water has the highest possible water potential because water molecules will flow from it to any other aqueous solution' no matter how dilute.
Apparatus
Apple corer – to cut circular potato pieces
Potatoes – to use to show osmosis
Kitchen towel – to dry potato pieces, so water does not make them weigh more, as this would not make it fair
5 test tubes – to put the solution in
Sucrose solutions – to put potatoes in, 5 different concentrations
Test tube rack – to put test tubes in
Pen, Paper and ruler - to record results
Electronic balance – to weigh potato pieces, gives a more accurate result than normal balance
Method
1. Take 2 similar sized main-crop potatoes.
2. Carefully use an apple corer to make circular sections approx. 2cms long.
3. Wash and dry all the pieces
4. Make a table to record results in.
5. Weigh each potato piece on an electronic balance and make sure they are a similar mass. Do this for 3 pieces at a time to ensure pieces for each solution do not get mixed up. You need to keep all the pieces together so you can keep track of which masses go into each test tube. This is important to keep the experiment a fair test.
6. Take a test tube rack and place 5 test tubes in it. Label them 0 molars, 2 molars, 4molars, 6molars, 8molars and 10molars
7. Using a measuring cylinder measure and pipette out different amounts of the sucrose solution and distilled water, which is poured into the test tubes in a percentage ratio giving you the various molar concentrations.
8. Put 3 potato segments into each beaker and leave for 24hours.
9. Dry with kitchen towel and re-weigh each segment on an electronic balance.
10.Record the results then make an average.
11. Re do using a second set of potato chips.
I have repeated the experiment to check for consistency and also because it ensures the results are fair and allows me to have a more accurate view on the changes. I have also worked out averages because I only require one set of results. As I was working with averages a control was not needed.
Results
First set of results
Second set of results
Average
Conclusion
In the 1st experiment, as the concentration got higher, generally, the mass of the potatoes got lower, but the graph did not end up as a sigmoid curve which it is supposed to look like. In the 2nd experiment, as the concentration go higher, the mass of the potatoes got lower. The graph looks more like a graph with a sigmoid curve in but still, it is not exactly right, even though I did everything to make it a fair test and get the most accurate results.
My prediction is half correct. In some cases it is correct because the concentration is higher and the mass of the potato is lower, but in other cases the mass of the potato gets higher, which I did not predict. For example, on the 1st experiment at 2 and 4 concentrations the mass of the potato goes up and the same happens on the 2nd experiment at the 6% concentration.
Evaluation
We followed the plan correctly, I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis.
My final results were very reliable, due to the precautions I took to make this a fair test.
To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the test tube to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. Therefore, we would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as we can.
We also could have got more people to do the experiment with us, so that we can organize the tasks, and we would be able to divide the tasks.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution.
Overall I am very pleased with my investigation and the way I carried it out.