Callie Hitchcock Osmosis and Diffusion Lab

Callie Hitchcock Osmosis and Diffusion Lab

(M are %) / Group 1 / Group 2 / Group 3 / Group 4 / Group 5 / 6th pd average / Jr. class average / Expected %
Distilled Water / 13.8 / 18.8 / 20.0 / 7.7 / 13.9 / 15.0 / 21.4
0.2 M / 5.7 / 7.6 / 11.1 / 9.9 / 10.5 / 8.6 / 6.9
0.4 M / 6.4 / 13.0 / 3.7 / 0.0 / 1.9 / 5.8 / -4.5
0.6 M / -21.8 / -21.6 / -30.9 / -13.9 / -22.4 / -22.5 / -12.8
0.8 M / -25.9 / -21.2 / -25.5 / -25.6 / -25.5 / -24.6 / -23.0
1.0 M / -17.9 / -22.4 / -32.7 / -30.2 / -30.7 / -31.2 / -26.8 / -23.5

Osmosis Part A

Analysis: One of the errors for this lab was that when our potatoes were put in 0.6 M water, they lost water weight. But the expected results show that the potatoes should have started diffusing water out of the cell by 0.4 M. Possible reasons for this may be that the potatoes were not blotted enough before weighing them the seccond time, or the potatoes were possibly very dry. Also the molarities of the solution might not have been exact.

1.3
(M are %) / Group 1 / Group 2 / Group 3 / Group 4 / Group 5 / 6th pd average / Jr.class
average / Expected %
Distilled Water / -4.2 / 0.0 / 0.0 / -1.3 / -0.6 / -1.3 / 1.2
0.2 M / 0.0 / 4.0 / 4.4 / 1.5 / 3.0 / 2.5 / 3.1
0.4 M / 7.7 / 8.0 / 8.6 / 11.1 / 9.9 / 8.9 / 7.7
0.6 M / 9.1 / 6.8 / 11.7 / 11.7 / 9.2 / 11.0
0.8 M / 10.8 / 11.1 / 16.0 / 16.0 / 16.0 / 13.5 / 14.8
1.0 M / 14.8 / 19.1 / 8.2 / 12.0 / 20.0 / 13.4 / 14.8 / 18.2

Conclusion: Knowing that osmosis is the movement of water from high concentration to low concentration, we can see from our data that the potatoes gained weight when put in distilled water, 0.2 M water, and 0.4 M water, but begins to lose weight as soon as the sucrose molarity of the water is 0.6 M. This means that when the potato was in the distilled water to 0.2 M water, the solution was hypotonic, while at 0.6 M the potato gave up its own water to try to create an equilibrium in the hypertonic solution. A weakness is that we had no way to double check the molarities and see if they were exact. With the possibility of dry potatoes, next time we could be them fresh the day of. Experimenters should also make sure to blot the potatoes thoroughly and make sure to peel all the skin off the potato cylinders.

Osmosis Part C

Analysis: One of the errors of this lab was that for distilled water the % change was supposed to be positive when the 6th period and Junior class average came out negative. This could be a result of the tap water we used intsead of distilled. Group one found 0.0% change when the dialysis bag was in 0.2 M which is wrong because some of the 0.2M water should have gone into the bag based on what we know about osmosis. This could be a result of blotting the bag too much or one of the ties might have been loose and some of the water could have leaked out. An error in my group was that we did not fill the bags with 25 mL of our solution, we filled it up with a random amount which could have affected our results.

Conclusion: Because osmosis is the movement from high to low concentration, the higher concentration, 0.2 M through 1.0 M sucrose, moved inside the dialysis bag with a semi-permeable membrane and distilled water (low concentration) like a cell, causing the dialysis bag to weigh more when checked the next day. Our results show that when there was a higher molarity of sucrose on the outside of the cell (dialysis bag) the higher concentration moved into the dialysis bag where there was lower concentration. To fix some of the problems in the analysis, we could have tied the bags tighter and more secure or been careful not too blot the dialysis bags too much or too little. A limitation of the experiment is that we did not have distilled water, so we didn’t have as much of an accurate reading as we could have. Next time we maybe could save up for some distilled water to make the experiment more accurate. My group should also use the beakers to measure out 25 mL instead of accidently filling the dialysis bag with a random amount.

Osmosis Part B

Drawing on separate sheet

Analysis: Errors were possibly not seeing the section where the saltwater had flooded too, therefore getting an inacurate representation of the flooded epidermis cell. It is uncertain whether what we were looking at was flooded with the right fluid because we didn’t know what we were looking for.

Conclusion: When the onion cell was flooded 15% NaCl salt water the cells that once looked clear were now magenta. The fresh water they started with had left the cell because it was higher free water concentration and moved to the are of lower free water concentration (the salt water flooded cell) and thus the pigment of the cell condensed to form the pink cell we saw. Some of the cells looked plasmolyzed and looked like the plasma membrane had shriveled and pulled away from the cell wall because of its presence in the hypertonic solution. With fresh water the cell looked the same as the seccond slide which I think was an error on our parts for not looking in the place where the cell was fresh water flooded. We should have tried harder to flood the entire epidermis with salt water and fresh water when asked to do so in the directions. A weakness was not being able to identify if we were sketching the right part of the cell with the solution because the cell was not totally covered in each solution each time. We were limited with our knowledge of what we were supposed to see. Next time we should study the cells and how they are supposed to look before the experiment, to make sure we are looking at the right thing.