Carbon Dioxide from Respiration by steepslope9876

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									   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.

								
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