Question

When a strong acid is neutralized by a weak base is the neutralization complete? Write the neutralization reaction for HClO4 and NH3. What is the value of Kn (equilibrium constant for neutralization)? (Kb(NH3)=1.810‒5) If stoichiometric amounts of acid and base are reacted will the resulting solution be acidic, basic or neutral?

Answer 1

Sol :-

Neutralization reaction is :

HClO₄ (aq) + NH₃ (aq) -----------------> NH₄⁺ (aq) + ClO₄^- (aq)

Since, HClO₄ is strong acid, therefore it will 100% ionized as :

H⁺ (aq) + ClO₄ (aq) + NH₃ (aq) -----------------> NH₄⁺ (aq) + ClO₄^- (aq)

and

Net ionic equation of neutralization reaction after the cancellation of spectator ion ClO₄^- on both side is :

H+ (aq) + NH3 (aq) -----------------> NH4+ (aq) , Kn = ?

As equation of K_b of NH₃ is :

NH₃ (aq) + H₂O (l) <----------------> NH₄⁺ (aq) + OH^- (aq) , K_b = 1.8 x 10^-5 ..............(1)

Also,

H⁺ (aq) + OH^- (aq) <---------------> H₂O (l) , 1/K_w = 1/1.0 x 10^-14 ..............(2)

The neutralization can be obtained by adding equations (1) and (2).

Therefore,

K_n = K_b/K_w

K_n = 1.8 x 10^-5/1.0 x 10^-14

K_n = 1.8 x 10⁹

As, the value of K_n is very large therefore, concentration of NH₄⁺ (strong conjugate acid of weak base NH₃) starts increases as equilibrium will shifts towards products side. So, pH < 7 and it will be acidic.