Write the Ka and Kb reactions of NaHCO3.
The Correct Answer and Explanation is :
The reactions involving the dissociation of NaHCO₃ (sodium bicarbonate) in water can be represented by its equilibrium constants, Ka and Kb.
1. Ka Reaction (Acid dissociation):
Sodium bicarbonate acts as a weak acid when it donates a proton (H⁺). The equilibrium for this reaction is as follows:
HCO₃⁻ (aq) ⇌ H⁺ (aq) + CO₃²⁻ (aq)
The Ka for this reaction can be expressed as:
[
Ka = \frac{[H⁺][CO₃^{2-}]}{[HCO₃^-]}
]
2. Kb Reaction (Base dissociation):
Sodium bicarbonate can also act as a weak base when it accepts a proton. In this case, bicarbonate reacts with water to produce OH⁻ (hydroxide ions) and H₂CO₃ (carbonic acid):
HCO₃⁻ (aq) + H₂O (l) ⇌ H₂CO₃ (aq) + OH⁻ (aq)
The Kb for this reaction is expressed as:
[
Kb = \frac{[H₂CO₃][OH⁻]}{[HCO₃^-]}
]
Explanation:
Sodium bicarbonate (NaHCO₃) is a salt derived from a weak acid (carbonic acid, H₂CO₃) and a strong base (NaOH). When NaHCO₃ is dissolved in water, it dissociates into sodium (Na⁺) and bicarbonate ions (HCO₃⁻). The bicarbonate ion can either act as a weak acid or a weak base, depending on the conditions.
- As a weak acid, bicarbonate can donate a proton (H⁺) to form carbonate (CO₃²⁻), which is represented by the Ka equation.
- As a weak base, bicarbonate can accept a proton from water, forming carbonic acid (H₂CO₃) and hydroxide ions (OH⁻), as shown in the Kb equation.
The values of Ka and Kb are related by the ion product of water (Kw):
[
Ka \times Kb = Kw
]
Since the pKa of bicarbonate is around 10.3 and the pKb is approximately 3.6, NaHCO₃ is a weak buffer with a significant ability to resist changes in pH.
Let me generate the visual representation for you.
Here is the visual representation of the Ka and Kb reactions of sodium bicarbonate. The diagram illustrates the dissociation of bicarbonate into its acidic and basic forms, with their respective equilibrium equations. Let me know if you need further details or clarifications!
