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The Chemistry of CO₂

  • Page ID
    3059
  • Chemical Concept Demonstrated

    • Chemistry of CO2

    Demonstration

    The three beakers contain limewater (Ca(OH)2).
    1. A student blows into the first beaker with a straw.
    2. Dry-ice is added to the second beaker.
    3. Club soda is added to the third

    Compare.

    co2.gif

    Observations

    1. A cloudy white precipitate forms.
    2.& 3. At first, a precipitate forms in the beaker. When additional dry ice and club soda are added, the precipitate redissolves.

    Explanations (including important chemical equations)

    Carbon dioxide dissolves in water and slowly reacts with water to produce carbonic acid.

    CO2 (g) + H2O (l) <=> H2CO3 (aq)

    The cloudy white solution observed when CO2 is bubbled into limewater results from a reaction between Ca(OH)2 and either CO2 or H2CO3 to form an insoluble calcium carbonate precipitate.

    Ca(OH)2 (aq) + H2CO3 (aq) <=> CaCO3 (s) + 2 H2O (l) Ksp = 2.8 x 10-9

    Excess CO2 or H2CO3 , however, reacts with the CO3 2- ion in this solution to form HCO3 -.

    H2CO3 (aq) + CO3 2- (aq) <=> 2 HCO3 - (aq)

    Since calcium bicarbonate is soluble in water, the CaCO3 precipitate dissolves in the presence of excess carbonic acid.

    CaCO3 (s) + H2CO3 (aq) <=> Ca 2+ (aq) + 2 HCO3 - (aq)

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