Chemistry Matter and Change, Florida Edition

 
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Teachers Notes:

Equilibrium Lab activity: Calcium Carbonate Equilibria

Problem 1:
1. K_eq = [H₂CO₃]
                [CO₂]

2. K_eq = [H⁺][HCO₃^-]
                [H₂CO₃]

3. K_eq =       [CO₂]           
              [Ca⁺²][HCO₃^-]²

4. K_eq = [Ca⁺²][HCO₃^-]²
                   [H₂CO₃]

Problem 2:
K_eq =         [CO₂]         
           [Ca⁺²][ HCO₃^-]²

To solve for the K_eq , one must know the concentration of CO₂, Ca⁺², and HCO₃^-.

Problem 3:
Aragonite is more soluble because the Ksp value is higher.

K_sp = [Ca⁺²][CO₃^-]

For calcite 4.5 x 10^-9 = [Ca⁺²][CO₃^-]. [Ca⁺²]= [CO₃^-] = x.

4.5 x 10^-9 = x x = 6.7 x 10^-5M = [Ca⁺²] = [CO₃^-]

For aragonite 6.0 x 10^-9= [Ca⁺²][CO₃^-]. [Ca⁺²]= [ CO₃^-] = x.

Problem 4:
(basic) CaCO₃ + H₂CO₃ → Ca⁺² + 2HCO^-₃ (acidic)

According to the Le Chatlier's principle, an equilibrium system will shift to relieve a stress applied to the system. The acidic environment in the water surrounding hydrothermal vents causes the calcium carbonate to dissolve in the snail shells because of a shift in equilibrium to the soluble acid side of the equilibrium system.