To demonstrate that the aqueous solution of hydrogen carbonate (HCO3-) is basic, we can consider the equilibrium reaction of the bicarbonate ion with water.
HCO3- + H2O ⇌ H2CO3 + OH-
In this reaction, bicarbonate ion (HCO3-) reacts with water to form carbonic acid (H2CO3) and hydroxide ion (OH-). The hydroxide ion is responsible for the basic nature of the solution.
To further analyze the basicity of the solution, we can consider the equilibrium constant expression (Kw) for the reaction of water self-ionization:
Kw = [H+][OH-]
In pure water at 25°C, the concentration of hydroxide ions (OH-) and hydrogen ions (H+) are equal and can be represented as [OH-] = [H+]. Therefore, we can rewrite the expression as:
Kw = [H+]^2
Now, let's examine the dissociation of carbonic acid (H2CO3) in water:
H2CO3 ⇌ H+ + HCO3-
The concentration of hydrogen ions produced by the dissociation of carbonic acid can be denoted as [H+]. Since H2CO3 is a weak acid, it only partially dissociates, and a portion of the bicarbonate ion (HCO3-) remains in the solution. The presence of hydrogen ions (H+) increases the concentration of [H+] in the solution.
Considering the equilibrium reaction between bicarbonate ion (HCO3-) and water:
HCO3- + H2O ⇌ H2CO3 + OH-
The formation of hydroxide ions (OH-) results from the reverse reaction of the dissociation of carbonic acid. As a result, the concentration of hydroxide ions increases, contributing to the basicity of the solution.
In summary, the presence of hydroxide ions (OH-) resulting from the equilibrium reaction between bicarbonate ion (HCO3-) and water demonstrates the basic nature of the aqueous solution of hydrogen carbonate (HCO3-).