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Carbon Dioxide In Solution. The Baking Soda Example. CO 2 Gas is In Equilibrium with Aqueous CO 2. CO 2 g ↔ CO 2 aq [CO 2 ]aq is proportional to the partial pressure of CO 2 Reduce gas pressure, it comes out of solution (soda)
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Carbon Dioxide In Solution The Baking Soda Example
CO2 Gas is In Equilibrium with Aqueous CO2 • CO2g ↔ CO2aq • [CO2]aq is proportional to the partial pressure of CO2 • Reduce gas pressure, it comes out of solution (soda) • Increase pCO2, it goes into water (green house effect on oceans)
Aqueous CO2 is In Equilibrium with Carbonic Acid H2CO3 • CO2aq + H2O ↔ H2CO3 • CO2 is an acid anhydride (add water, you get acid!) • Equilibrium lies far to the left • Carbonic anhydrase
Carbonic Acid H2CO3 is In Equilibrium with Bicarbonate Ion HCO3- • H2CO3↔ HCO3- + H+ • Bicarbonate is the conjugate base of the free acid carbonic acid • At low pH H2CO3 is formed, but rapidly breaks down to give CO2 gas • At neutral pH HCO3- is predominant and no gas is observed
Bicarbonate Ion HCO3- is In Equilibrium with Carbonate CO32- • HCO3-↔ CO32- + H+ • Carbonate is the conjugate base of Bicarbonate • At neutral pH HCO3- is predominant and stays in solution • At high pH CO32- is predominant and forms precipitate
Figure 1. Titration of 5% Sodium Bicarbonate With 1 M HCl [HCO3-] [HCO3-] = [H2CO3] [H2CO3] rapidly dissociates to CO2 gas and water
Behavior pH Changes little with addition of acid Bubbles deplete CO2 pH change accelerates