Dialysis Biology Lab Report

Dialysis Biology Lab Report

31
Lab 7 – Dialysis
Introduction
Have you ever known someone undergoing hemodialysis? Have you ever sprayed a bottle of air
freshener, cologne, or perfume, and noticed the fragrance slowly filling the room? Did you
know that the same scientific principle is behind both of these processes?
Diffusion occurs when any molecules move in a direction that lowers the concentration (such as
fragrance molecules spreading throughout a room). Osmosis is similar to diffusion, except that
only water molecules are moving, and they move across a semi-permeable membrane, such as a
cell membrane to equalize the concentration of solutes on each side of the membrane. Semipermeable membranes allow only small molecules to pass through them (such as urea, oxygen,
water, and ions). Although the net movement of ions or water will be to areas of lower
concentration, it is important to remember that there is a constant, balanced flow of ions and
water in both directions. Larger molecules such as starches (glucose polymers), proteins, and
fats are unable to pass through the small holes in the membranes.
Dialysis occurs naturally in our kidneys or artificially through hemodialysis or peritoneal
dialysis. During dialysis, small unwanted waste chemicals such as urea or sodium diffuse from
high concentrations in our blood to lower concentrations in the kidneys or artificial dialysate
solution. This diffusion occurs across a semi-permeable membrane, which keeps larger
molecules such as proteins from being removed from the blood. This waste is then removed in
urine. Water is also removed from the blood, passing across the membrane by osmosis.
When the kidneys have failed (lost 80-90% of function), artificial dialysis is performed.2

Hemodialysis was first used as a regular treatment in the 1960s. In hemodialysis, a patient is
connected to an artificial kidney, known as a hemodialyzer. Blood containing large amounts of
waste products is removed from the patient and passed outside the body through dialysis tubing
in the hemodialyzer. Outside of the tubing is the dialysate solution, which contains little or none
of those same chemicals. The undesirable waste chemicals diffuse out of the blood, across the
membrane, and into the dialysate. (Image from Reference 3.)

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If it is desirable to add small chemicals to the blood (such as bicarbonate to counteract blood
acidosis), high concentrations of these chemicals can be added to the dialysate. They then
diffuse through the membrane into the blood. Artificial dialysis takes time, usually around four
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hours at each appointment. Larger molecules like red blood cells remain in the blood and return
to the patient. The net result is that water and waste are UePRYed fURP Whe SaWieQW¶V bRd\. SiQce
the waste chemicals can only be removed through dialysis, dialysis is performed about three
times per week.
In Part C, several characterization tests will be used to test for
the movement of chemicals during dialysis. Change in pH will
be used to test for the movement of bicarbonate ions.
BenedicW¶V WeVW will be used to test for glucose, with solids (see
right for colors) indicating a positive test and the sugar
concentration. The iodine test will be used to test for starch,
with a dark blue/purple color indicating a positive test for the
presence of starch. To test for the movement of chloride (and
presumably sodium) ions, silver nitrate will be added and will form a white precipitate (solid),
AgCl if chloride (Cl-) is present.
NaCl(aq) + AgNO3(aq) Æ AgCl(s) + NaNO3(aq)
Topics and terms to refer to in your textbook
Solute, solvent, solution, diffusion, semi-permeable membrane, osmosis, dialysis,
suspension
ASK
x What chemicals can move across a dialysis tube membrane, and which direction can they
move (in/out)?
ACQUIRE – Experiment
Chemicals Equipment
0.1 M silver nitrate (aq) 100, 250, 400, 600 mL beakers
Benedict’s solution 6 150 mm (medium) test tubes
iodine reagent (>10%) 12 100 mm (small) test tubes
3% (m/v) sodium bicarbonate Pipet
5% (m/v) sodium chloride
1 piece dialysis tubing (15 cm long) ± soaking
in water for at least 15 minutes
3% glucose string (2 pieces, 15 cm long)
1% starch stirring rod
red food coloring 25 mL graduated cylinder
Funnel
Hot plates
pH paper
squirt bottle, containing distilled water
SAFETY NOTES: Wear safety goggles and closed toe shoes at all times. BeQedicW¶V
solution is basic. Rinse immediately with water if you get it on your skin.
WASTE NOTES: Test tubes from Part C containing silver nitrate should be disposed
of in the designated waste container. All other solutions can be poured down the drain.
Benedict͛s test results
0% m/v sugar Remains clear blue
0.5% m/v sugar Green solid
1% m/v sugar Yellow solid
1.5% m/v sugar Orange solid
2% m/v sugar Brick red solid
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INSTRUCTOR DEMO: Part A – Dialysis with sodium bicarbonate as the dialysate
1. Use pH paper to measure the pH of distilled water and 3% (m/v) sodium bicarbonate.
Then fill a dialysis tube with distilled water and one drop of red food coloring. Lay the
sealed tubing in the bottom of a beaker, and fill the beaker with 100 mL of 3% (m/v)
sodium bicarbonate.
2. After 40 minutes have passed, test the pH of the bicarbonate solution in the beaker using
pH paper. Remove the dialysis bag from the bicarbonate solution, and rinse it with
distilled water. Carefully set it in a clean beaker, then cut the top of the bag off. Measure
the pH of the solution inside of the bag using pH paper. Post data on the board for the
class.
STUDENTS START HERE
Part B – Dialysis with sodium chloride, glucose, and starch as simulated ³blood´
Note: Any solution that contains starch should be shaken before every transfer or testing.
1. Obtain six large test tubes. Label them 1-6.
Blood (in tubing) Dialysate (surroundings)
Test tube 1 Test tube 2 Test tube 3 Test tube 4 Test tube 5 Test tube 6
Blood
BEFORE
Blood
AFTER
At 40 min
Surroundings
BEFORE
(pure water)
Surroundings
At 1 min
Surroundings
At 20 min
Surroundings
At 40 min
2. In a 100 mL beaker, mix 5 mL of 5% sodium chloride, 5 mL of 3% glucose, 5 mL of 1%
starch solution (shake the starch!), and one drop of red food coloring. Once this is done,
mix the solutions together using a glass stirring rod. This initial red solution will
UeSUeVeQW a diaO\ViV SaWieQW¶V bORRd. Pour 5 mL into test tube 1 (Blood BEFORE).
3. Obtain a wet piece of dialysis tubing from the class supply. Note: Work quickly as the
dialysis tubing will become difficult to handle as it dries out. Tightly tie a string about
one inch from one end of the dialysis tubing. Using your fingers or tweezers, gently open
the other end of the dialysis tubing and
place a glass funnel into the opening. Mix
the initial red solution with a glass stirring
rod, then pour about 10 mL of it through
the glass funnel and into the dialysis
tubing. Try to avoid getting any of the red
solution on the strings. Once this is done,
use another string to tie a firm knot at the
open end. Rinse the tied tubing with
distilled water. Lay the tied tubing on the
bottom of a 250 mL beaker.
4. Pour 5 mL of distilled water into test tube 3 (Surroundings BEFORE). Pour additional
distilled water into the beaker until the tubing is completely covered with the water
(about 100 mL). Make a note of the time.
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5. Now, carefully and quickly pour 5 mL of the surrounding water into a medium test tube
4 (Surroundings 1 MIN). After 20 minutes, pour 5 mL of the surrounding water into test
tube 5 (Surroundings 20 MIN), and after another 20 minutes (for a total of 40 minutes,
Surroundings 40 MIN), pour 5 mL of the surrounding water into test tube 6.
6. Carefully cut the tied tubing open at one end, and pour at least 5 mL of the contents into
test tube 2 (Blood AFTER).
Part C – Identification of solutes in dialysis solutions
1. Prepare a boiling water bath in a 400 mL beaker (fill it about half-way with tap water).
Start with the hot plate at a high setting, and lower it once the water boils.
2. You should have six medium test tubes containing solutions. Take test tube 1 and pour
1 mL of the solution into a clean, small test tube. Then pour another 1 mL of solution
into a second small test tube. Repeat with test tubes 2-6, so that you have a total of 18
test tubes, as shown below. Use test tube racks to stay organized.
Blood (in tubing) Dialysate (surroundings)
Test tube 1 Test tube 2 Test tube 3 Test tube 4 Test tube 5 Test tube 6
Blood
BEFORE
Blood
AFTER
At 40 min
Surroundings
BEFORE
(pure water)
Surroundings
At 1 min
Surroundings
At 20 min
Surroundings
At 40 min
3. Now perform tests to determine what is in each solution. Record your observations for
each characterization test, including if the test is positive or negative. Be descriptive in
your observations.
a) Glucose identification: For the 6 medium test tubes, add 2
mL of BenedicW¶V VROXWiRQ to each test tube. Place the test
tubes into the hot water bath for five minutes. In a test that
is positive for glucose, you will see a solid form that is
similar to those in the table to the right. Record your
observations.
b) Starch identification: For another group of 6 small test tubes, add 2 drops of iodine
test solution to each test tube. In a test that is positive for starch, the solution will turn
dark blue.
c) Chloride identification: For one group of 6 small test tubes, add 2 drops of AgNO3 to
each test tube. In a test that is positive for chloride, a white solid will form.
Ag+ (aq) + Cl- (aq) Æ AgCl (s)
18 total test tubes
3 mL solution + Benedicts
(glucose test)
1 mL solution + Iodine
(starch test)
1 mL solution + AgNO3
(chloride test)
Benedict͛s test results
0% m/v sugar Remains clear blue
0.5% m/v sugar Green solid
1% m/v sugar Yellow solid
1.5% m/v sugar Orange solid
2% m/v sugar Brick red solid
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Lab 7 – ACQUIRE – Data Name: _____________
Partner: ________________
Part A Data ± from INSTRUCTOR DEMO:
Sketch the beaker, dialysis bag, the chemicals present and arrow to show
the direction of their movement in the beaker to the right.
Blood (in tubing) Dialysate (surroundings)
Blood
BEFORE
Blood
AFTER 40 min
Surroundings
BEFORE
Surroundings AFTER
40 min
pH meas
Part C
Sketch the beaker, dialysis bag, the chemicals present and arrows to show
the direction of their movement in the beaker to the right.
Data (include brief observations and if the test was positive or negative)
Blood (in tubing) Dialysate (surroundings)
Test tube 1 Test tube 2 Test tube 3 Test tube 4 Test tube 5 Test tube 6
Blood
BEFORE
Blood
AFTER
At 40 min
Surroundings
BEFORE
(pure water)
Surroundings
At 1 min
Surroundings
At 20 min
Surroundings
At 40 min
Glucose
(3 mL in test
tube, plus 2
mL Benedicts
solution)
Starch test
(1 mL in test
tube, plus 2
drops iodine)
Cl- test
(1 mL in test
tube, plus 2
drops
AgNO3)
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APPRAISE – Discussion
1. Answer each of the questions we ASKED. Your answer should include specific chemical
names, data from parts A and C, and comments on the rate of diffusion, direction of diffusion,
and size/polarity of the solutes moving.
What chemicals can move across a dialysis tube membrane, and which direction can they
move (in/out)?
2. Ask a follow-up question to this experiment, and briefly describe an experiment that could
answer that question.
References
1. Frost, L; Deal, T.; General, Organic, and Biological Chemistry, An Integrated Approach, 1st ed.; Pearson:
New Jersey, 2011; pp 271-273
2. ³NaWiRQaO KidQe\ FRXQdaWiRQ. http://www.kidney.org/atoz/content/dialysisinfo.cfm. (accessed June 23, 2012)
3. Merck Manual Home Health. http://www.merckmanuals.com/home/kidney_and_urinary_tract_
disorders/dialysis/dialysis.html. (accessed July 16, 2012)
4. Kidney Disease of Diabetes. http://www.kidney.niddk.nih.gov/KUDiseases/pubs/kdd/index.aspx.
(accessed July 31, 2013).