The rate at which you breathe bears a relationship to the carbon dioxide in your body.
Perhaps you have observed that during exercise the heart rate and breathing rate increases. Does
the increased muscular activity cause this? Does the body breathe faster because the body
"needs" oxygen? How does the body "know" when to increase the breathing rate? Could this be
a function of carbon dioxide? These are some of the questions you may be able to answer after
completing this laboratory exercise.
        In this lab lesson, you will use a method of measurement called TITRATION to
determine the amount of carbon dioxide exhaled under different conditions. Since one molecule
of carbon dioxide is released for every molecule of oxygen consumed, the measurement of
carbon dioxide is a good indicator of the respiration rate of an organism. You will use a unit
called a MICROMOLE for your calculations. A micromole is one millionth of a MOLE, a unit
used most often in che mistry.

Beaker, 250 ml                       Test tubes
Erlenmeyer flask, 250 ml             Measuring pipette, 2 ml
Soda straws                          Phenolphthalein
Sodium hydroxide 0.04%               Sodium hydroxide 0.01N
Hydrochloric acid 0.1N

        Count your breathing per minute while relaxed in a sitting position. Do this three times
and calculate the average. 1.) What is your average breathing rate per minute?
        Obtain from the stock table 5 mls of 0.04% NaOH Solution and 5 mls of dilute HCl (1N).
Pour the NaOH into one clean test tube and the HCl into another test tube. Add one drop of
phenolphthalein to each test tube and note the reaction. 2.) How does the phenolphthalein react
to the NaOH, a base? 3.) How does it react to the acid, HCl? Discard the material from the
tubes in the sink and wash the test tubes.
        Pour exactly 100 mls of distilled water into a clean Erlenmeyer flask. Add 5 drops of
phenolphthalein. If the water does not turn pink, add several drops of the 0.1N NaOH until the
solution turns a VERY faint pink. Swirl the solution and let stand for 30 seconds. The pink
color must remain; if not, continue to add NaOH. Hold the flask against a white background and
note the shade of pink obtained. You will need to duplicate the original shade of pink later. This
is the most critical comparison in the lab and that is the reason you will want to make the
solution just faintly pink.
        Exhale into the pink solution through the soda straw for EXACTLY one minute. Try to
breathe as closely to normal as possible. 4.) Record the number of exhales during the minute.
From the stock table, obtain about 50 mls of the 0.04% NaOH solution in a beaker. With a 10 ml
graduate, measure 3 mls of the 0.04% NaOH and add to the flask into which you exhaled one ml
at a time. Gently swirl. When the pink color disappears, add additional 0.04% NaOH one ml at
a time using a graduated pipette. Continue to add and swirl until your ORIGINAL color of pink
is obtained and remains for 30 seconds. NO NOT PASS THIS END POINT! That is, do not
have the pink any darker than your original faint pink. 5.) How many total milliliters of the
0.04% NaOH were needed to turn your flask pink? Multiply this number of mls by 10 and you
will have the number of micromoles of carbon dioxide you exhaled into the flask in one minute.
6.) How many micromoles of carbon dioxide did you exhale at rest?
        Discard the material in the flask and rinse with tap water. The other partner should now
repeat the above procedure.

         Hold your breath as long as you are able without being too uncomfortable. 7.) Record
this time of breath holding. Prepare the flask with the water and phenolphthalein using the same
procedure as in Part One. After you have returned to your normal rate of breathing, hold your
breath once more. This time, after breath holding, exhale through the straw into the prepared
flask. This will be difficult and you will lose some of the exhaled air through the sides of your
mouth. This will not ruin the experiment if you attempt to hold this loss to a minimum and
breathe mostly into the straw for one minute. Be sure to count the number of breaths exhaled
into the flask. Your partner can best do this. 8.) Why is this count important? 9.) From your
observations, did the time it took the color to go from pink to colorless occur faster in Part One
of the lab or in this part? 10.) How many micromoles of carbon dioxide were produced and
released after breath holding?
         Discard the material in the flask and rinse with tap water. The other partner should not
repeat the above procedure.

         Prepare the flask for this last experiment in this exercise as was done in Parts One and
Two. This time HYPERVENTILATE for one minute or until you feel dizzy, whichever occurs
first. Immediately AFTER hyperventilation, exhale into the flask as before. It is very important
in this part of the exercise to exhale ONLY AS YOU FEEL THE NEED to do so. Continue to
exhale for ONE minute as before. 11.) How many breaths did you exhale into the flask in the
one- minute after hyperventilation? 12.) How many micromoles of carbon dioxide did you
release in the one-minute after hyperventilation? The other partner should now complete the
         Compare the data as to the number of breaths and how much carbon dioxide was
produced as the result of each of the three conditions. 13.) Graph this data as directed by your
         14.) After graphing your individual results, write a brief paragraph INTERPRETING the
relationship between your RATE of breathing and the amount of carbon dioxide in your body as

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