Method:
- Find a potato
- Using a cork borer, take a cylinder-shaped slice out of the potato, of roughly 5 cm in length
- Then using a razor and a white tile, cut the skin off of each end
- Next, cut the piece into two 2cm lengths using a ruler
- Any excess from the cylinder can be thrown away
- Repeat this four times, until you have ten 2cm pieces of potato
- Weigh each one and write their weights down in a table
- Put two into each test tube and write the number on it with a black marker pen
- You should now have five test tubes with two pieces of potato in them each
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Using a measuring cylinder, pour into each test tube 10cm3 of NaCl solution. Each solution should be at a different concentration: 0.1, 0.15, 0.2, 0.25 and 0.3 (measured in molars of NaCl)
- Now leave the five test tubes for twenty four hours
- Gently, tip the solution out of the test tube and down the drain
- Next, delicately place the individual cylinders of potato onto a piece of tissue and roll them on it, allowing all excess moisture to dry off
- Take care not to allow the potato to break or to dry all the moisture out of them
- Finally reweigh the potato pieces, record the information, noting down which cylinder of potato came from where. Then find the average for the osmosis through different salt molar solutions using the two results for each concentration that you obtained.
Apparatus:
- White tile – for cutting on
- Razor Blade – to cut the potato pieces
- Distilled water – part of the experiment
- Cork borer – to cut out the potato cylinder pieces
- Tissue Paper – to dry the potato pieces after the experiment
- Electronic Weighing Scale – to weigh the individual pieces
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10 cm3 Measuring Cylinder – for measuring the solutions
- Potato – main part of the experiment
- Five Test Tubes – for the experiment
Factors affecting the experiment:
- Surface Area – the greater the surface area, the faster osmosis can occur
- Whether the ends of the cylinder are cut off – osmosis cannot occur through the skin of the potato, and so unless the ends are cut off, the surface area through which osmosis can occur will have been reduced
- Different Potatoes – each potato has different concentrations of each substances depending on where, when and how it was grown and so different potatoes can produce different results
What I expect to happen:
Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration of either two substances.
So, when the salt concentration is higher in the tissue, the water will leave the tissue of the potato, and the potato will lose weight. And if there is very little different in the two water concentrations, there shouldn’t be such a big change in weight. And if there is a lower concentration of salt in the potato, the water will leave the potato.
In this particular experiment, I believe that pure salt solution is of higher concentration than that of the potato, so at 1.0 molar the water will leave the potato and enter into the solution, making the potato lose weight and shrink.
At 0.8 molars, I believe the case to be the same, and that water will enter the solution, but at 0.6 or 0.4 molars, I believe the salt concentrations will be roughly the same and so the weight and size of the potato will remain the same.
Finally at 0.2 molars and with distilled water, I expect that the concentrations will be the complete opposite of before: The potato will contain a higher salt content than the distilled water and so water will travel through the membrane of the potato and increase the size and weight of the potato.
Previous Research:
Previously, I did a preliminary experiment to establish a range of experimental solutions. I applied the same method as above except I used a different range of concentrations: 0, 0.2, 0.4, 0.6, 0.8, 1.0. From the results of this preliminary experiment, I established that the point where no osmosis occurs is around 0.15 molars of NaCl solution. So when I repeated the experiment, my range was narrowed down to 0.1, 0.15, 0.2, 0.25 and 3.
Results:
From my results, one can see where the exact point is where no osmosis occurs. You can see that as the concentration of NaCl goes up, the potato pieces stop gaining water, and start losing water.
Conclusion:
I am very happy with these results as my objective was accomplished successfully and I had no trouble with the experiments. My results are very close to what I predicted, as I predicted that the point where osmosis would no longer occur would be roughly 0.2 molars, when it was nearer 0.18. I think my results came out right as I executed the experiment with a lot of planning and precision.
Bibliography:
