What is the Ka
reaction of HCN?
reaction:
Incorrect The
of HCN is
The Correct Answer and Explanation is:
The correct acid dissociation reaction for hydrogen cyanide (HCN) is:
HCN(aq) ⇌ H⁺(aq) + CN⁻(aq)
This equation represents the ionization of HCN in water, where HCN releases a proton (H⁺) and forms its conjugate base, the cyanide ion (CN⁻).
Given that the acid dissociation constant (Ka) for HCN is 6.2 × 10⁻¹⁰, the base dissociation constant (Kb) for CN⁻ at 25°C can be calculated using the relationship:
Ka × Kb = Kw
where Kw is the ionization constant of water at 25°C, equal to 1.0 × 10⁻¹⁴. Solving for Kb:
Kb = Kw / Ka Kb = (1.0 × 10⁻¹⁴) / (6.2 × 10⁻¹⁰) Kb = 1.61 × 10⁻⁵
This value represents the basicity of CN⁻, showing its ability to accept a proton in aqueous solution.
Hydrogen cyanide is a weak acid, meaning its dissociation in water is minimal compared to strong acids. The small Ka value confirms this low level of ionization. The cyanide ion, as the conjugate base, has a relatively high Kb, indicating a significant tendency to attract protons. This explains why CN⁻ can act as a strong nucleophile in chemical reactions, making it useful in organic synthesis.
Understanding acid-base equilibria helps predict reaction behavior in aqueous solutions. The relationship between Ka and Kb provides insight into the strength of acids and bases, allowing determination of pH and reactivity. Calculating these constants is essential in fields such as environmental chemistry, biochemistry, and industrial applications, where acid-base interactions influence processes like buffer formation and metal extraction.
This explanation connects theoretical principles with practical applications, making acid-base chemistry relevant beyond academic study.
