Identify the two conjugate acid-base pairs in the following reaction:

Question

HCl(aq) + NH3 (aq) NH 4  

+(aq) + Cl-(aq) 

 __________/__________ ___________/____________ 

Answer 1

Hello,

Let's recall the Bronsted Lowry definition of an acid and base. A Bronsted Lowry acid is a proton donor, while Bronsted Lowry base is a proton acceptor. Now, we look at the reaction equation. Which reactant donates its proton (H+)? HCl does, donating the H+ and ending up as Cl- on the product side. Conjugate base is the chemical formed when an acid donates its proton, so Cl- is the conjugate base. Now, on the reactant side, which reactant will accept a proton and end up with one more H+ on the product side? NH3 does, which accepts the proton that HCl donates, forming NH4+. This makes NH3 the base (the proton acceptor) in this reaction. The conjugate acid, which is formed after accepting a proton from the acid, is then NH4+.

In short,

acid/conjugate base pair: HCl/Cl-

base/conjugate acid pair: NH3/NH4+

Hope this helps.