Is NH4 An Acid Or Base? Strong Vs Weak - Ammonium Ion

When ammonia reacts with proton donors like H+ or H3O+, it formed an ammonium ion. 

⇒ H+ + NH3 → NH4+

And when ammonium ion reacts with proton acceptor like OH–, it returns to the neutrally charged ammonia molecule.

⇒ NH4+ + OH– → H2O + NH3

The ammonium ion has the ability to donate the proton because there is no lone pair present on the central atom in the NH4+ molecule which can be used to accept the proton from other compounds. Thus, the only ability left for ammonium ion is “donating the proton”.

Whereas NH3 molecule has lone pair on the central atom that can be used to accept the proton and as per Bronsted-Lowry base “a base is the substance that accepts the protons from other species”. 

An acid is something that produces protons when dissolved in an aqueous solution. So, when an ammonium ion is dissolved in an aqueous solution, it split into two ions (NH3 and H+).

⇒ NH4+ → NH3 + H+

We have two most important acid-base theories to check whether NH4+ is an acid or base in nature.

(a). Arrhenius theory

(b). Bronsted-Lowry theory

⇒ Arrhenius theory:- 

This theory tells if any compound can release the proton when dissolved in an aqueous solution, qualify as acid and if any compound can release the hydroxide ions when dissolved in an aqueous solution, qualify as the base.

So, in the case of ammonium ion, when dissolved in water, it is ready to “give off” the proton. Hence, we can say, NH4+ is an Arrhenius acid.

⇒ Bronsted-Lowry theory:-

This theory tells if any compound can donate the proton to other species and forms a conjugate base, qualify as acid. And for base nature, it’s vice-versa.

So, when NH4+ reacts with hydroxide ion, it donates the one proton to OH– and forms a conjugate base(NH3). 

As per the above reaction, NH4+ act as Bronsted-Lowry acid and release a proton to become NH3, and OH- acts as Bronsted-Lowry base as it accepts the proton and forms H2O.