CARBON DIOXIDE AND HUMAN BREATHING INTRODUCTION 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. MATERIALS 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 LABORATORY PROCEDURE PART ONE - NORMAL BREATHING 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. PART TWO - BREATH-HOLDING 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. PART THREE - HYPERVENTILATION 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 exercise. 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 teacher. 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 shown BY YOUR GRAPH.
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