Ahmet Tuğrul AKKUŞ
DIALYSIS
Design
Research Question
Which of sucrose, sodium chloride and sucrose are capable of diffusing through the selectively
permeable membrane to the water solution?
Variables
No dependent and independent variables exist since the experiment relies on observations and no
graphical interpretation of data needed.
Controlled Variables
1) Temperature (°C)
2) Mass of samples (g)
3) Volume of water in the dialysis tubing (ml)
4) Time interval between taking the samples (min)
5) Same type of water (tap water)
6) Volume of water in the beaker (ml)
Apparatus
1) Starch
2) Glucose
3) Sodium chloride
4)15 cm dialyzing tube
5) Glass rod
6) Cotton thread
7) 3 test tubes
8)100 cm3 beaker
9)600 cm3 beaker
10) Dropping pipette
11) Test tube rack
12) Test tube holder
13) Bunsen burner
14) Tripod
15) Gauze
16) Matches
17) Stopwatch
18) Iodine solution
19) Silver nitrate solution
20) Benedict solution
21) Gloves
22) Tap water
23) Ruler
24) Scissor
25) 100 ml Graduated cylinder
26) Water bath
Dialysis tubing allows the selective diffusion of molecules or ions of different sizes across a selectively
permeable membrane. In this experiment certain masses of sucrose, starch and sodium chloride are
used to test their capability of passing through the dialysis tubing.As sucrose is a disaccharide and
starch is a polysaccharide, it is known that these molecules are too large and complex to be able to pass
through the dialysis tubing. On the other hand, sodium chloride will dissociate into ions in the solution
and chloride ions will be able to pass through the dialysis tubing.
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First step was to make sure all needed apparatus were on the desk in the order they are
needed.
By the help of the ruler a 15.0 cm length of dialysis tubing was cut by the help of scissor and
uncertainty was noted down (+- 0.1 cm)
The dialysis tubing was wet under the tap water and glass rod was used to open the tubing
Dialysis tubing was knotted in one end of the tubing by cotton thread
Using mass balance 4.00g of sucrose, starch and sodium chloride was taken with an
uncertainty of (+- 0.01 g) and was put into the 100 ml small beaker.
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50 ml of tap water was added to the 100 ml small beaker by the help of 100 ml graduated
cylinder with an uncertainty of (+- 0.5 ml)
The mixture was stirred with stirring rod.
Then mixture was added to the dialysis tubing, as it would take too much time to do it with a
dropper and time was limited, mixture was directly poured from the small beaker into the
dialysis tubing.
After pouring the mixture, a thread of cotton was tied around the open end.
Outside of the dialysis tubing was washed under tap water.
400 cm3 of water was used as a water bath and it was filled with water and placed on the
Bunsen burner with the gauze, by the help of matches the water bath was started to be heated.
The dialysis tubing was placed into the large 600 cm3 beaker and it was filled with tap water
up to the level of knot.
The stopwatch was started immediately and three samples were taken by the Pasteur pipette
to the separate 3 test tubes. Test tubes were labeled and they were used for the test of certain
samples
TEST TUBES
TEST FOR
1)
Chloride ion
2)
Starch
3)
Sucrose
(Table 1.1)
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Few drops of silver nitrate solution was added to the test tube 1 and if chloride ions had passed
through the selectively permeable membrane, then there would be a white precipitate as a
result of silver chloride forming.
Few drops of iodine solution were added to test tube 2 and if the solution contains starch, the
solution will have a blue/ black color.
Few drops of Benedict solution were added to third test tube and the test tube was placed into
the water bath by using the test tube holder. If the sucrose was able to pass through the
selectively permeable membrane into the water, then with the help of heating green, yellow or
red color would occur depending on the amount of sucrose present in the water. If it is not
present, solution will be blue which the color of Benedict solution is.
Every five minutes three samples were taken and the same test was applied for each.
At the end of 25 minutes, drops of iodine solution was added to the solution beaker and looked
for any presence of starch.
Here a table is drawn for the results gathered form the samples for 6 trials in the 25 minutes in the
experiment.
Time/min
For Chloride ions
For starch molecules
For Sucrose molecules
0
No change
No change
Blue color
5
White ppt.
No change
Blue color
10
White ppt.
No change
Blue color
15
White ppt.
No change
Blue color
20
White ppt.
No change
Blue color
25
-
No change
-
(Table 1.2)
The table 1.2 is sufficient enough for the interpretation of the data about the relationship between the
sizes of molecules or ions and their capability of passing through the selectively permeable membrane
but a table giving information about the diameter of molecules and ions will be helpful to support the
results gathered from the experiment.
Particle
Diameter/nm
Water Molecule
27.5
Chloride Ion
0.362
Iodide Ion
0.452
Sucrose Molecule
102.9
Starch Molecule
17500.0
(Table 1.3)
(Reference to http://answers.yahoo.com/question/index?qid=20081023104732AAxRLlH)
If the results of the experiment and the information in table 1.3 are combined, the interpretation will
be much more explanatory.
CONCLUSION
For chloride ions, in the first trial (at the very beginning of the experiment), there was no white
precipitate which makes us sure that there is not chloride ion present in the water at the very
beginning so the first trial is a control group for the experiment. From 5 th minute to 20th minute, white
precipitate occurred in the addition of silver nitrate solution in all 5 trials. This proves that chloride
ions are capable of passing through the selectively permeable membrane and also If we look at the
diameter of a chloride ion, it is considerably small to others which enables it to pass out of the dialysis
tubing.
For starch molecules, there was no change in the color of samples when iodine solution was added,
which indicates that starch molecules are not capable of passing through the selectively permeable
dialysis tubing. Also, the diameter of a starch molecule is 17500.0 nm which is considerably larger than
other molecules or ions so it supports the idea that starch molecules are too big to pass through the
selectively permeable membrane. The first sample was a control group.
For sucrose molecules, all the samples were blue and it was the color of Benedict solution added to test
tubes so it was clear that sucrose molecules was not able to pass through the selectively permeable
membrane to the water neither. The molecular diameter of sucrose is 102.9 nm which disables it from
passing through the dialysis tubing into the water. The first sample was a control group.
There could be some improvements to the experiment.
ü Using distilled water instead of tap water
ü Measuring the mass of the dialysis tubing with the mixture in it at the beginning of the experiment
and the volume of water used in the 600 cm3 beaker and then measuring the final mass of dialysis
tubing at the end of 25 minutes to look for changes caused by the diffusion of water molecules from
outside water solution to the dialysis tubing and diffusion of chloride ions from dialysis tubing to the
water.
ü Using Fehling’s solution for the test of sucrose instead of Benedict.
ü Having more effective Bunsen burners and time for the test for sucrose
ü Repeating the experiment one more time
As a conclusion, the experiment showed that sucrose and starch molecules cannot pass through the
selectively permeable membrane where as chloride ions can, the reason for this ability or disability is
about their molecular sizes. Sucrose is a disaccharide and starch is a polysaccharide so they are large
molecules where as chlorine ions are considerably smaller than these.