Question

The first and second dissociation constants of an acid H₂A are 1.0 × 10⁻⁵ and 5.0 × 10⁻¹⁰ respectively. The overall dissociation constant of the acid will be ______.

विकल्प

• 0.2 × 10⁵

• 5 × 10⁻⁵

• 5 × 10¹⁵

• 5 × 10⁻¹⁵

Answer 1

The first and second dissociation constants of an acid H₂A are 1.0 × 10⁻⁵ and 5.0 × 10⁻¹⁰ respectively. The overall dissociation constant of the acid will be 5 × 10⁻¹⁵.

Explanation:

\[\ce{H2A <=> H^+ + HA^-}\]

∴ K₁ = 1.0 × 10⁻⁵ = `(["H"^+]["HA"^-])/(["H"_2"A"])`

\[\ce{HA^- <=> H^+ + A^-}\]

∴ K₂ = 5.0 × 10⁻¹⁰ = `(["H"^+]["A"^-])/(["HA"^-])`

For the reaction, \[\ce{H2A <=> 2H^+ + A^{2-}}\]

K = `(["H"^+]^2["A"^(2-)])/(["H"_2"A"])` = K₁ × K₂

= (1.0 × 10⁻⁵) × (5.0 × 10⁻¹⁰)

= 5 × 10⁻¹⁵