The base ionization constant, K_b, of ammonia in water is 1.8 × 10^-5. The value of the acid ionization constant, K_a, of the conjugate acid, is closest to

Explanation:-

For the ammonia (NH₃) and its conjugate acid ammonium ion (NH₄⁺), we have the following equilibrium reactions in water:

NH₃ + H₂O ⇌ NH₄⁺ + OH^-

• The base ionization constant, K_b, is given as 1.8 × 10^-5.
• It represents the equilibrium constant for the reaction of ammonia with water to form ammonium ions and hydroxide ions.
• The acid ionization constant, K_a, for the conjugate acid ammonium ion (NH₄⁺), is related to K_b through the following expression:

K_a × K_b = K_w

• where K_w is the ion product constant for water at a given temperature, which is approximately 1.0×10^-14 at room temperature.
• The value of Ka can be calculated as follows:

Ka × Kb = Kw

or, K_a × (1.8 × 10^-5) = 1.0 × 10^-14

or, K_a = (1.0 × 10^-14) / (1.8 × 10^-5)

or, K_a ≈ 5.6 × 10^-10

• So, the value of the acid ionization constant, K_a, of the conjugate acid (NH₄⁺) is approximately 5.56 × 10^-10.

Conclusion:-

Hence, the value of the acid ionization constant, Ka, of the conjugate acid, is closest to 5.6 × 10-10