Results:
Prediction:
I predict that as osmosis is the movement of liquid from a high concentration to a low concentration through a semi permeable membrane that the lower the concentration of sugar solution, the larger the mass of the potato in the test tube.
Apparatus: (And there use.)
Cork Borer – To cut out the cylindrical shape
18 Test Tubes – To hold the solution and potatoes
Potatoes – To cut out the cylindrical shapes
18 cylinder shaped potatoes - To investigate osmosis using potatoes.
Test tube racks – To hold the test tubes
Measuring cylinder – To get exact quantities of the liquids
Sucrose Solution – To use as a variable
Water – To use as a variable
Scales – To get the exact weight of the potato.
Paper Towels - To dry the potato
Stop Clock – To time 30mins as that is how long the experiment is.
Precautions:
Take care when cutting the potato as the cork borer is sharp and could cause an injury. When touching the potatoes make sure hands are dry to avoid contamination with water or sugar solution.
Variables:
To create a fair test I have to keep certain parts of the experiment the same while one variable changes. I have chosen to vary the concentration of sugar solution. This will hopefully give me a detailed set of results from which I can make an adequate conclusion. I have to make sure that all liquids are measured correctly and the potatoes weighed to a significant degree of accuracy so my results will contain no anomalies. I will measure in cm3 and grams. I will always use the same scales and make sure all potatoes weigh about 1.62 grams and that I measure before and after the experiment.
Method:
- Collect all equipment needed.
- Using a cork borer, cut out 18 cylindrical shaped potato cells.
- Weigh them using the same scales all the time so they are 1.62 grams. (Cut or re-make if too less or too much.)
- Dry the potatoes off using a paper towel.
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Using a measuring cylinder, measure out 10 cm3 of sucrose solution.
- Place the liquid into a test tube, and label “100%.”
- Then repeat steps 5 and 6 twice for the same amount of each liquid.
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Then repeat steps 5, 6 and 7 for 80%, (2 cm3 of water and 8 cm3 of sucrose solution), 60%, (4 cm3 of water and 6 cm3 of sucrose solution), 40%, (6 cm3 of water and 4 cm3 of sucrose solution), and 20%, (8 cm3 of water and 2 cm3 of sucrose solution).
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Also produce three test tubes of just water (10 cm3.).
10.) Place all dried potato shapes into the test tubes and set the stop clock for 30 minutes.
11.) After 30 minutes, dry the potatoes and weigh them. (Be careful not to mix the potatoes up.)
Diagram:
Conclusion:
The graph on the previous page shows the osmosis of a potato using the axes, mass and % concentration. The graph has a sharp decline and the points are fairly widespread. As the amount of concentration is increase, the intake of water decrease. Therefore, decreasing the amount of sugar solution, the intake of water increases.
There are roughly two points for each concentration which seem to be located in the same area. The other point can vary + or – ten grams. These are my anomalous results and are circled in red pen. As my points vary the line of best fit would not be a curve. This shows that my graph isn’t too accurate and could be caused from the amount of time the potato was left in the water. The only water potatoes decreased in mass because osmosis couldn’t happen as they wasn’t a variety of concentrations.
I predicted that as osmosis is the movement of liquid from a high concentration to a low concentration through a semi permeable membrane, that the lower the concentration of sugar solution, the larger the mass of the potato in the test tube. My graph shows this quite clearly even though there are a few strange results.
If I could make another prediction, I would state that:
“In a reasonable amount of time such as 30 mins, I predict that the lower the concentration of sugar solution, the larger the mass of the potato.”
Evaluation:
When I said in my prediction that the lower the concentration of sugar solution, the larger the mass of the potato, it was only true up to a point. On my graph, at 60% concentration, the result was 1.87 grams. This is in between the 40% concentration at 1.86 and 1.88 grams. Also on my graph, a 100% concentration result is shown at 1.78 grams which is higher than 80%. All the other points support my prediction.
In my further prediction stated in the conclusion, I said that “in a reasonable time such as 30 mins…” I put this because in my experiment I didn’t have time to carry out all trials for the full 30 mins. One trial was accurate and another had 5 mins left where the final one had 15 mins still remaining. The three water trials had only been in the test tubes for 10 mins. If I had carried out the experiment to the full time period, then the results would have been accurate and precise.
At 60% concentration, two trials were at 1.59 grams and 1.69 grams but the final one was at 1.87 grams. This is a strange result as they should be closer together. Also 1.64 grams at 40% concentration was strange as it was too low compared to the others at 1.86 and 1.88 grams. All the 100% concentrations are spread out from 1.78 to 1.48 grams with 1.58 grams in between. The strangest results can be seen in the 80% concentration trials. Two are below the line of best fit while another is above. Also, 1.46 and 1.49 grams are lower than the 100% concentration.
Experimental errors were also made, some being random and some being systematic. A systematic error was that we didn’t record the start mass of each potato. They were roughly measured at 1.62 grams but not everyone was this weight. This will affect the graph and results as the percentage change will not be accurate as it will be taken from the average. The occasional errors occurred in the solution measurement but wouldn’t have affected the results to a noticeable extent.
As I had quite a few anomalous results I would carry out a few more trials but concentrate particularly on the 80% concentration as I was surprised with the results.
If I repeated this experiment, I would make sure that I included the start mass as this would give me a more accurate measure of percentage change. I would also carry the experiment out over the full 30 mins and this would mean that my results would be precise. I would also make sure that the potatoes were dry before measuring them.
To extend this experiment I would add more concentrations to have a wider spread of results and I would use different time scales. This would further my prediction.
