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) Increase pCO 2, it goes into water (green house effect on oceans)

Aqueous CO 2 is In Equilibrium with Carbonic Acid H 2 CO 3 CO 2 aq + H 2 O ↔ H 2 CO 3 CO 2 is an acid anhydride (add water, you get acid!) Equilibrium lies far to the left Carbonic anhydrase

Carbonic Acid H 2 CO 3 is In Equilibrium with Bicarbonate Ion HCO 3 - H 2 CO 3 ↔ HCO H + Bicarbonate is the conjugate base of the free acid carbonic acid At low pH H 2 CO 3 is formed, but rapidly breaks down to give CO 2 gas At neutral pH HCO 3 - is predominant and no gas is observed

Bicarbonate Ion HCO 3 - is In Equilibrium with Carbonate CO 3 2- HCO 3 - ↔ CO H + Carbonate is the conjugate base of Bicarbonate At neutral pH HCO 3 - is predominant and stays in solution At high pH CO 3 2- is predominant and forms precipitate

Table 1. Titration of 5% Sodium Bicarbonate With 1 M HCl μL Base AddedpHChanges 08.5Yellow Bubbles Bubbles Bubbles Red Color

Figure 1. Titration of 5% Sodium Bicarbonate With 1 M HCl

[HCO 3 - ] [HCO 3 - ] = [H 2 CO 3 ] [H 2 CO 3 ] rapidly dissociates to CO 2 gas and water

Behavior pH Changes little with addition of acid Bubbles deplete CO 2 pH change accelerates