Understanding the Dissociation of H Ions from 1 Mole of Sodium Bicarbonate in Excess Water

The dissociation of H ions from 1 mole of sodium bicarbonate (NaHCO?) in excess water involves a complex interplay of chemical equilibria and the autoionization of water. This article aims to explore this process, providing insights into the behavior of the bicarbonate ion in solution and the impact on the pH of the solution.

Chemical Equilibria and pH

The bicarbonate ion (HCO??) is an ampholyte, meaning it displays both acidic and basic properties. In aqueous solution, the bicarbonate ion can react in two ways:

HCO?? H?O ? H?CO? OH? HCO?? H?O ? H?O? CO?2?

Additionally, there is the fundamental water autoionization equilibrium:

H?O ? H?O? OH?

The complex interplay of these equilibria is responsible for the pH of the solution being 8.3. It is important to note that both reactions 1 and 2 are generally shifted to the left, with the following approximate equilibrium constants:

K? ≈ 10?11 (for the reaction with H?O)

K? ≈ 10 (for the reaction with H?CO?)

Calculating CO?2? Concentration

To determine the concentration of CO?2? ions produced by equilibrium 1, we can use the following formula:

[CO?2?] cK?K?/([H?O?]2 K?[H?O?] K?K?)

For a 0.1 M solution of NaHCO?, where c is the analytical concentration of bicarbonate and K? and K? are the constants of the first and second ionizations of H?CO?, we can find:

[CO?2?] ≈ 9.3 x 10?? M

Comparing this with the [H?O?] concentration, which is (5.0 times 10?? M) (due to the pH of 8.3), it is clear that the concentration of CO?2? is much lower than H?O?.

Implications for the Dissociation of H Ions

Given the above, if 1 mole of sodium bicarbonate dissociates, 1 mole of H? ions is produced from the bicarbonate. However, the precise number of dissociated H? ions attributable to equilibrium 1 is difficult to determine due to the complex interplay of the various equilibria.

Ignoring any additional H? and OH? ions from the autoionization of water, the dissociation of 1 mole of NaHCO? would theoretically produce 1 mole of H? ions. However, the balance of the solution's pH and the concentration of H? ions are influenced significantly by the other equilibria described.

Thus, understanding the dissociation of H? ions in such systems requires a detailed knowledge of the specific equilibria involved and how they interact to maintain the overall pH of the solution.