Kelce Gerlits
Osmosis and Diffusion Lab
Processed Data:
(Raw Data can be found attached as Appendix A)
Dialysis Bag Results (Osmosis Part C)
4th period 4th period
Group 1
Group 2
Distilled water -4.2
0
0.2 M
0
4.0
0.4 M
7.7
8.0
0.6 M
9.1
6.8
0.8 M
10.8
11.1
1.0 M
14.8
19.1
(See Appendix C for graphs)
6th period
Group 3
0
4.4
8.62
11.7
16
12
6th period
Group 4
-1.22
1.5
11.1
16
20
Expected Class average
1.2
3.1
7.7
11.0
14.8
18.2
3.3
8.9
9.2
13.5
14.8
Percent Change in Potato Core Results (Osmosis Part A)
Group 1
Group 2
Group 3
Group 4
Expected
(in %)
(in %)
(in %)
(in %)
(in %)
Distilled
13.8
18.8
20
20
21.4
water
0.2 M
5.7
7.6
11.1
6.9
0.4 M
6.4
13.0*
-3.7
-4.5
0.6 M
-21.8
-21.6
-30.9
-12.8
0.8 M
-25.9
-21.9
-25.5
-25.0
1.0 M
-17.9
-27.4
-30.2
-30.2
-30.7
*Outlier, due to possible contamination (See Appendix B for graphs)
Cell Osmosis (Osmosis Part B)
Before NaCl (Initial)
Addition of NaCl
Visible, block-like cell walls. Cell walls are blurry and
pushed together.
(Magnification 40x) (See Appendix A for sketches)
Class
average (%)
15
8.5
3.9
-22
-24
-27.8
Removal of NaCl (Flood)
Cells are not much more
clear, however the block
and wideness of the cell has
returned.
Data Analysis:
(Osmosis Part C)
The experiment titled Dialysis Bag, was conducted with a small plastic bag filled
with sucrose and tied with strings at the end of each side, then placed into a beaker filled
with water. An error that may have occurred during this experiment could be that the
bag had a hole in it, or the strings weren’t tied tightly enough, therefore allowing the
sucrose in the bag to seep into the water and ruining the experiment. (See Appendix C
for graph of the data)
(Osmosis Part A)
The experiment using a potato core was conducted by first coring a potato, then
placing it in several beakers with different concentrations of sucrose, ranging from
distilled water (no sucrose) to 1M of sucrose solution. Error found in this experiment was
when the solutions were being poured into beakers. Due to the amount of solution,
beakers, and people in the process of conducting this experiment, solutions could have
been mixed due to the mixing of measuring items, which could have tampered and
ruined the outcomes of the experiment.
(Osmosis Part B)
Error found in this experiment with the onion cells was the process of preparing
the slide. Some of the onion skins could not have been sliced enough which did not allow
much observation, or the slide could have been messed up as well with the addition of
water and/or NaCl.
Conclusion and Evaluation:
(Osmosis Part C)
The data in this lab indicates that due to osmosis, water will diffuse into the low
concentration gradient found in the plastic baggy filled with various levels of sucrose
solutions, to the high water concentration gradient of water the baggy was immersed in.
For example, as shown in the data table, at .2M sucrose solution in the plastic bag (the
selectively permeable membrane), the class found an average of a 3.3% mass increase.
Also, when the bag contained a concentration of .8M of sucrose solution, the average
mass gain was 13.5%.
A limitation found in this experiment would be time, because our group rushed to
finish this section of the lab before class was over, and ended up ending two or so
minutes early. This would not skew the data greatly, however it still may have.
Some weaknesses found were shared materials, and the materials used. The
solutions, beakers, and funnels used in this experiment all ran the risk of being cross
contaminated, which could be changed by giving each group their own set of
instruments. Another weakness found was the risk of the plastic baggy actually leaking
due to the string not being tied tight enough or a whole in the baggy. This could be fixed
by finding different materials that still provide the same purpose.
(Osmosis Part A)
The expected values, along with the majority of the class values, show that potato
cores absorb liquid under the concentration of about .2M of sucrose, because after .2M
on the table, the percentages are negative. For example, at .2M of sucrose, the potato’s
mass increase according to the class average was 8.5%, whereas the potato’s mass
increase at .6M of sucrose solution was -22%. These numbers help us further understand
osmosis in a real life situation. The potato is a root, which means it grows underground,
and so when it is watered it has to absorb the water faster than the dirt around it. Proven
by the data in this lab, potatoes have a very low molarity of water, so when water is
added to the potato and around the potato, it will absorb it up because of the potato’s
low water concentration and water’s attraction to low concentrations due to osmosis.
A limiting factor found in this lab was the amount of time. This cannot really be
helped since we can only devote so much time to labs at school, however if we put aside
more days or time to work on this lab, it would eliminate the problem.
A weakness found in this lab is the lack of the group’s own solutions and beakers,
which runs the risk of cross contamination. One way to improve this would be to give
every group each their own separate kit.
(Osmosis Part B)
This lab displays the osmosis process in an onion cell. The onion cells were
observed as normal, then immersed in a solution of NaCl, and then observed again. The
difference in the cells before and after was great, the cells shriveled upon entry of NaCl,
due to diffusion. However, when the cells were flushed with water again after the NaCl
was added, the cells returned to normal size due to osmosis. This lab can be used with
the same observation as the potato lab. The onion is also a root as well, so it would have
to absorb the water before the dirt around it did. This lab also shows that the onion easily
takes water into its cells before any other substances such as NaCl.
A weakness found in this lab was that the class viewed the cell at only 40x, versus
the recommended 100x. However, the process could still be easily viewed and observed
under 40x.