Transcript Carbon Dioxide from Respiration

Carbon Dioxide from
Respiration
Carbon dioxide from respiration is
demonstrated by two chemical
reactions
PURPOSE
To demonstrate that carbon dioxide is
expelled from the lungs by seeing it
react with limewater (calcium
hydroxide) and bromothymol blue
indicator
DEMONSTRATION:

When carbon dioxide is blown through a
straw into a flask of limewater (calcium
hydroxide) the carbon dioxide reacts with
the solution to produce insoluble calcium
carbonate. When the same is done with
bromothymol blue indicator, the carbon
dioxide turns the solution from blue to
yellow-green.
CONCEPTS:

Respiration

Solubility

pH

Indicators
RESPIRATION

Respiration is the ventilation of the lungs
(breathing) and the exchange of gases
between blood and the atmosphere. The
exchange of gases occurs in the alveoli of
the lungs in which oxygen is loading and
carbon dioxide is unloading. In this
demonstration, the carbon dioxide used for
chemical changes was produced by
respiration.
SOLUBILITY

The solubility of a substance is the amount of that
substance that can be dissolved in a given quantity
of solvent. In this demonstration the reaction of
the carbon dioxide and limewater produced a fine,
white precipitate of calcium carbonate. The
reason a precipitate formed is because calcium
carbonate is insoluble in water. Calcium carbonate
is limestone (chalk is a finely-grained calcium
carbonate).

CO2(g) + Ca(OH)2(l)
CaCO3(s) + H2O(l)
pH and INDICATORS


Bromothymol blue is an indicator that turns
yellow-green in the presence of acidic substances.
When carbon dioxide is breathed into water it
reacts with the water to form carbonic acid.
CO2 + H2O
H2CO3
Carbonic acid itself is in equilibrium with water
and carbon dioxide.
 As more and more carbonic acid is produced, the
pH of solution decreases causing the indicator to
change color to yellow-green. The color change
of the indicator thus serves to demonstrate the
presence of carbon dioxide by showing the change
in pH.
CONCLUSION
The carbon dioxide produced from respiration was used
to do chemical reactions which demonstrated its
presence. The reaction of carbon dioxide and calcium
hydroxide produced calcium carbonate which was
insoluble in water and formed a white precipitate.
As the carbon dioxide reacted with the water in the
bromothymol blue indicator, the pH decreased (became
more acidic) causing the blue color to change to
yellow-green.
COMMENTS

You can also use dry ice with the same
effects for the source of carbon dioxide in
this experiment,
Fun Facts

Carbon dioxide does not burn or support
combustion. Because of this property, it is
used in some fire extinguishers.