The Carbon Dioxide Acid Breath Test
The Carbon Dioxide Acid Breath Test
Carbon dioxide (CO2) is a colorless gas. It’s responsible for giving soda its fizz and
plants use it for photosynthesis. We use oxygen to burn fuel for energy and CO2 is a
product of that process that we breathe out. CO2 levels in the air are very low, however,
in a closed environment such as a space shuttle, the amount of CO2 may reach toxic
levels. The level of CO2 must be closely monitored and removed from the shuttle so
that it does not poison the astronauts. In this activity, you’ll learn how CO2 can affect
pH (how acidic or basic a substance is) and how to counteract this using a CO2
absorber.
Procedure:
1. Place the ‘Indicator Only’ flask on the stirplate and turn on the STIR (NOT HEAT)
knob so that the stir bar is slowly but steadily stirring your mixture. Move the flask
until the stir bar does not interfere with the pipette tip.
What is the color of the liquid in the flask? ___________________________
2. Take your balloon and blow it up but DO NOT TIE IT. Hold it tightly so the air
does not escape.
3. Take your straw and place it over the tip of the pipette which is inserted into the
stopper of your flask.
slowly
4. Place the end of your balloon over the straw and
loosen your grip so
that you can let the air enter into the straw. You can take turns with your own
balloon. The reaction is complete when you observe a color change. Once you
do you can stop. This color change alerts you that the solution has changed
from slightly basic to acidic.
What is the color of the liquid in the flask now? _____________________________
5. Now switch flasks. Turn off the stirplate. Carefully remove the ‘indicator only’
flask from the stir plate and replace it with the ‘indicator and absorber flask’.
What is the color of the liquid in the flask? ___________________________
The Carbon Dioxide Acid Breath Test
6. Slowly turn on the STIR knob so that the solution is stirring slowly.
7. Remove the rubber stopper and USING TONGS drop a small piece of dry ice
into this second flask then quickly replace the rubber stopper. Dry ice is solid
CO2. Since you’re probably out of breath, you’re using dry ice instead of blowing
into the flask.
8. Watch the liquid in the flask. Do you see a color change?
What is the color of the liquid in the flask? ___________________________
The chemical that is responsible for the color in the flasks is called phenolphthalein.
Use the chart showing the color of phenolphthalein at different pH values fill in the pH
range of each of the flasks before and after addition of CO2.
Indicator*only*
CO2#from#your#breath#
pH#range=________#
Indicator**
+*absorber*
pH#range=________#
Dry#ice#
pH#range=________#
pH#range=________#
Make Your Own Acid-Base Indicator…and Then Test It!
Make Your Own Acid-Base Indicator…and Then Test It!
pH is the measure of how acidic or basic a substance is. A pH indicator is a chemical
that changes color based on how acidic or basic a substance is. When the indicator
comes in contact with a substance, the indicator's color corresponds to that substance's
approximate pH, which is a scale of zero to fourteen (with zero being the most acidic,
seven being neutral, and fourteen being the most basic) that indicates the acidity or
basicity of a substance. Red cabbage contains a pH indicator. You will make a solution
of pH indicator and test the pH of various household products.
1. Obtain some of the red cabbage mixture in a cup. Place a coffee filter loosely
over a second cup and secure with a rubber band. Carefully pour the cabbage
mixture onto the filter. You should see only a deep reddish-purple liquid in the
second cup with no cabbage pieces.
2. The coffee filter with cabbage leaves can now be discarded in the trash. Save
the liquid as this is your indicator.
3. Obtain a 6 well plate. Choose six different commercial products and have
your teacher put a little in each well. Write down the name of which product is
in which well below. Get a variety of those from the ‘acid’ group and those from
the ‘base’ group.
Product"
1"
2"
3"
pH"
Acid"or"Base?"
1"
2"
3"
4"
4"
5"
6"
5"
6"
4. One at a time, pipette indicator one drop at a time until you see a color change.
GENTLY swirl the plate to mix everything.
5. Write down the color of each well after adding the indicator. Use the ‘Acid-Base
Color Chart for Cabbage Juice Indicator’ to estimate the pH of each product and
determine which are acids and which are bases.