Osmosis Lab
Aleksandar Nelson Nacev
Planning A:
Question: Is it possible to determine which substances will pass through a semi-permeable membrane, and how does the concentration gradient affect the rate of osmosis?
Hypothesis: By using dialysis tubing and the substances glucose, starch, albumin, silver nitrate, and sodium chloride, one will be able to determine which of these substances will pass through a semi-permeable membrane. By using differing concentrations of sucrose as a solute, one can determine the affect that concentration gradient has on the rate of osmosis.
Variables:
First
Section:
Dependent: The substances able to pass through a membrane
Independent: The substances used
Second
Section:
Dependent: The rate of osmosis
Independent: The concentration gradient of the solutions
Control: A solution of pure de-ionized water
Planning B:
First Section:
Materials:
· Two sections of Dialysis Tubing
· Four Pieces of String
· Two beakers
· Solutions of Glucose, Starch, Albumin, silver nitrate, sodium chloride
· Water
· 10 mL pipette and pipette pump
· Four graduated cylinders
· Four test tubes
Procedure:
1. Open each section of dialysis tubing and tie one end with a piece of string.
2. To one piece of tubing add 20 mL, using the graduated cylinders, of glucose, starch albumin and albumin. Then tie the other end shut with a piece of string.
3. To the other section of tubing add 20 mL of sodium chloride and tie the other end shut with a piece of string.
4. Add each section of tubing to separate beakers filled halfway with water. Label the beakers either combination or sodium chloride. Make sure not to submerge the end in which the substances were poured into due to contamination of the water.
1. Allow the tubing to set for five minutes.
2. Add 20 mL of silver nitrate to the sodium chloride beaker and record the visual results of both inside the tubing (relates to silver nitrate) and outside the tubing in the beaker(relates to sodium chloride).
3. Take three 3 mL samples of water solution outside of the tubing from the combination beaker and place into separate test tubes.
4. In one test tube use a glucose test strip to check for the presence of glucose. Record the results.
5. In another test tube add iodine to the solution to test for the presence of starch. Record the results.
6. In the last test tube add benedict’s testing reagent to test for the presence of protein. Record the results.
Second Section:
Materials:
· Six beakers
· Six sections of dialysis tubing
· Concentrations of .2 M, .4M, .6M, .8M and 1M of sucrose
· De-ionized water
· Graduated Cylinders
· Stopwatch
· String
Procedure:
1. Open each section of dialysis tubing and tie one end with a piece of string.
2. To each section of tubing add either de-ionized water, .2 M, .4M, .6M, .8M or 1M of sucrose. Then tie shut the other end of the tubing.
3. Weigh each section of tubing and record values as initial.
4. Obtain six beakers filled halfway with de-ionized water.
5. Place each tubing section in a separate beaker and start the stop watch.
6. At each five minute interval, remove the bags and weigh them recording the results.
Data Collection:
First Section:
Visual Results
|
Substance |
Visual Result |
|
Glucose |
No change on test strip |
|
Starch |
Remained an orange-yellow color |
|
Albumin |
Remained a blue color |
|
Silver Nitrate |
No precipitate inside of the tubing |
|
Sodium Chloride |
Precipitate present in beaker water |
Second Section:
Weight of Bags
|
Concentration |
Initial Weight (g) |
5 min Mark (g) |
10 min Mark (g) |
15 min Mark (g) |
20 min Mark (g) |
25 min Mark (g) |
30 min Mark (g) |
|
Water |
20.72 |
21.34 |
21.90 |
22.32 |
21.79 |
21.86 |
22.03 |
|
.2 M Sucrose |
21.08 |
22.65 |
23.47 |
23.78 |
24.24 |
24.34 |
24.11 |
|
.4 M Sucrose |
22.30 |
23.98 |
24.51 |
25.22 |
26.14 |
26.18 |
26.82 |
|
.6 M Sucrose |
22.36 |
23.96 |
24.80 |
25.93 |
26.32 |
26.95 |
27.53 |
|
.8 M Sucrose |
23.45 |
25.00 |
26.48 |
28.92 |
29.75 |
30.95 |
31.95 |
|
1 M Sucrose |
23.54 |
26.50 |
27.67 |
27.80 |
28.84 |
29.64 |
30.56 |
Data Analysis:
First Section:
· If glucose passed through, then the water outside the bag would change the test strips color.
· If starch passed through, then the water outside the bag would change to a dark blue when iodine was added.
· If albumin passed through, then the water outside the bag would change to a purple when the Benedict’s reagent was added.
· If sodium chloride passed through the membrane, then there would be precipitate outside of the dialysis tubing.
· If silver nitrate passed through then there would be precipitate inside of the dialysis tubing.
Analytical Results
|
Substance |
Visual Result |
Did the |
|
Glucose |
No change on test strip |
Negative |
|
Starch |
Remained an orange-yellow color |
Negative |
|
Albumin |
Remained a blue color |
Negative |
|
Silver Nitrate |
No precipitate inside of the tubing |
Negative |
|
Sodium Chloride |
Precipitate present in beaker water |
Positive |
Second Section:
Example:
Percent Change in Mass
|
Concentration |
0-5 min |
5-10 min |
10-15 min |
15-20 min |
20-25 min |
25-30 min |
|
Water |
2.992 % |
2.624 % |
1.918 % |
-2.375 % |
.3212 % |
.7777 % |
|
.2 M Sucrose |
7.448 % |
3.620 % |
1.321 % |
1.934 % |
.4125 % |
-.9449 % |
|
.4 M Sucrose |
7.534 % |
2.210 % |
2.897 % |
3.648 % |
.1530 % |
2.445 % |
|
.6 M Sucrose |
7.156 % |
3.506 % |
4.556 % |
1.504 % |
2.394 % |
2.152 % |
|
.8 M Sucrose |
6.610 % |
5.920 % |
9.215 % |
2.870 % |
4.034 % |
3.231 % |
|
1 M Sucrose |
12.57 % |
4.415 % |
.4698 % |
3.741 % |
2.774 % |
3.104 % |
Average Percent Change
|
Concentration |
Average Percent Change By Mass |
|
Water |
1.04% |
|
.2 M Sucrose |
2.30% |
|
.4 M Sucrose |
3.15% |
|
.6 M Sucrose |
3.54% |
|
.8 M Sucrose |
5.31% |
|
1 M Sucrose |
4.51% |
Conclusion and
Evaluation:
First Section:
When viewing the results of this lab, one can conclude that every substance except for sodium chloride was not allowed to pass through the dialysis tubing. Consequently in a plasma membrane only sodium chloride could pass through. All of the other substances, if wished to be utilized by the cell must be brought in by proteins. This test also proves the existence of proteins in a cell membrane. One knows that glucose must be brought into a cell for energy, however, the lipid bi-layer will not allow for glucose to pass through. Thus there must be certain proteins present which act as transport vehicles to allow glucose to enter the cell otherwise the cell would not be able to carry out cellular respiration. One source of error in this lab could stem from the fact that when the bags were placed into the beakers, if the tops of the bags, where the substances were poured into, touched the water, then the residue left from pouring could contaminant the water thus creating false positives. To help correct this issue, one should carefully place the bags into the water.
Second Section:
When our groups results for the average percent change of mass is compared to the class’s average for percent change of mass, one gets the table below.
Average Percent Changes of Mass Compared
|
Concentration |
Our Lab |
The Class Average |
|
Water |
1.04% |
0.530 % |
|
.2 M Sucrose |
2.30% |
2.75 % |
|
.4 M Sucrose |
3.15% |
4.74 % |
|
.6 M Sucrose |
3.54% |
6.23 % |
|
.8 M Sucrose |
5.31% |
9.46 % |
|
1 M Sucrose |
4.51% |
10.3 % |
When one compares the class data to our lab group’s data, there are some significant discrepancies. The lower concentrations are fairly similar, however, when reach .8 M and 1 M there is a significant difference in the average percent change by mass. Our peak rate of osmosis occurred in our .8 M solution, the class peak occurred in the 1 M solution. Therefore, our lab had a significant source of error somewhere. Unfortunately, I cannot recall our group performing the experiment with any major mistakes. Perhaps the temperature difference between the morning classes and the afternoon classes caused the significant change in data. Unfortunately I do not think I can be exactly sure what caused the discrepancy without going through the lab again, but taking the average of the class data does help even out the results.
