Biology 6.0
Organisms and pH lab
Names: _______________________________
_______________________________
_______________________________
Individual organism must maintain a relatively stable internal environment. Both
organsms and cells respond to many environmental factors that otherwise would
change their internal environment. One factor is pH which involves the relative
concentrations of Hydrogen and Hydroxide ions. The calculation to determine
pH or (percent of hydrogen) is represented by the -log [H+]. The general
concentrations of hydrogen ions range between 1.0 x 10-1 and 1.0 x 10-14.
These values give you the range in the pH scale from 1 to 14. Biochemical
activites of living tissues frequently affect the pH, yet life depends on maintaining
the pH range that is normal for each tissue or system. A buffer is a substance
that can be used to maintain a constant pH, meaning its pH does not change
with the addition of an acid or base. Buffers accomplish this by accepting excess
hydrogen ions (acidosis) or donating H ions (due to alkalosis). Substances that
make good buffers are those that are in the category of either a weak acid or a
weak base. Strong acids and bases do not accept and donate ions readily. An
example of a buffering system is the carbonic acid/ bicarbonate system that
maintain the constant pH of the blood.
Problem one: use the following buffering system to indicate how the pH of the
blood is maintained. Answer the questions below:
H2O + CO2  H2CO3  HCO3- + H+
[
Reaction A
]
[
Reaction B
]
The arrows going in both directions means that the reaction can go either way
depending upon the necessity.
Think about this situation.
1. _____________________. If someone is hyperventilating what gas are
they releasing at a faster rate than normal?
2. _____________________. How is your body going to replace that
depleting gas? (Which reaction will INITIALLY have to take place and in
which direction will it go?)
3. _______________. Write on the line the chemical that is NOW starting to
become lower in concentration because of the reaction in number 2.
4. ____________________. What reaction is now going to have to take
place in order to replace the lost chemical in number 3? (Again, which
reaction letter and which direction)
5. ________________. What compounds needed to combine in order to
make the compound for the answer in number 3?
6. Explain what is going to happen to the pH of this system if all of the
previous events are occurring. Will it increase? Decrease? And why?
____________________________________________________________
____________________________________________________________
____________________________________________________________
Problem Two: What effect does an acid have on a non-biological material such
as tap water? Pour 25 mL of tap water into a 50 mL beaker. Record the initial
pH of the tap water using Hydrion paper. Add .1M HCL a drop at a time, swirling
to mix the contents after each drop until 5 drops have been added. Record the
pH. Continue to add 5 additional drops and record the pH after each 5 drop
interval *Make sure to swirl before recording. Stop once you hit 30 drops in the
tap water. Fill in table one found at the end of this lab.
1. _____________ What is the initial pH reading?
2. ______________What is the final pH reading?
3. ______________Did the water’s pH increase or decrease as you added
HCL?
4. ______________In terms of concentration of Hydrogen, what was
the difference between your initial and final pH readings?
Problem Three: Repeat the same procedure as problem two, but this time use
.1M NaOH. Record your data in table one and answer the following questions.
1.________________ What is the initial pH reading?
2. _______________ What is the final pH reading?
3. _______________ In terms of concentration of Hydrogen (making
sure the answer is a positive number) what is the difference between the final
and initial pH?
4. _______________ Which substance, NaOH or HCl had more of an
effect on the pH of the water?
Problem Four: What effect does pH have on a biological material. In this part of
the lab you will be assigned on biological material which could be either potato,
liver, egg white, or warm gelatin.
Note: You will be testing this COLORED materials with hydrion paper
which relies on the change in color. Try your best to see a different in the paper
color due to pH not due to the substance you are putting on the strip.
______________________________  Our assigned biological material was….
Using the same method of 5 drops of HCl per interval and then in a separate trial
5 drops of NaOH, but instead of 25 mL of water you will need 25 mL of the
biological material.
Record your results in table ONE.
1. __________________. Initial pH before you added HCl.
2. __________________. Final pH after you added 30 drops of HCl.
3. __________________. In terms of concentration of H, how much more
acidic was the material after 30 drops?
4. __________________. Initial pH before you added NaOH.
5. __________________. Final pH after you added 30 drops of NaOH.
6. __________________. Difference in concentration of Hydrogen ions
before and after the addition of NaOH.
Once you have completed, add your data to the board and copy down data
from the other groups for the other three materials.
Problem FIVE: Now you are going to test an actual buffer for its capacity to
resist changes in pH. Use the same procedure with the HCl and NaOH and
record the results up to 30 drops.
1.____________________. Once you reached 30 drops, what was the
overall change in Hydrogen concentration?
Table One:
Solutions Tested
Drops added
Tap water
Biologial material
Buffer
pH after addition of .1 M HCl
0
5
10 15 20 25
30
pH after addition of .1M NaOH
0
5
10 15 20 25 30
Table Two:
Biological
Material
Initial reading
before HCl
Final Reading
after HCl
Initial Reading
before NaOH
Final
Reading
after NaOH
1. Create a bar graph which will compare the results of the biological substance
before and after the addition of the 30 drops of HCl and NaOH. (i.e – there
should be a bar for the pH of liver before any addition of HCl, a bar that has the
pH of liver after 30 drops of HCl, and a bar that has the pH of liver after 30 drops
of NaOH) You will use one bar graph to show all biological substances used.
Please use averages of the groups data. There should be a total of 12 bars on
your graph. 3 bars/biological material.
Summary Questions: In a cohesive paragraph, answer the following
questions. The order does not necessarily need to be the order in
which they are asked, but I should be able to tell that ALL questions
have been answered.
1. What biological material used in this lab responded the most to the
addition of HCl?
2. What biological material used responded most to the addition of NaOH?
3. Were the results of problem five, with the buffer system, more like the
results of the tap water or your biological material problems?
4. What might that say about the biological materials that you used?
5. In reference to problem one, what are individuals generally told to do
when they are hyperventilating such as on a plane or during a panic attack?
Why do you think they are told to do so? What is that doing for their body?