Salts and acids/ bases conceptual question

[gkangelexa]

My book says the following:

NH₄NO₃ is weakly acidic as a salt because it is composed of the conjugates of the base NH₃ and the strong acid HNO₃.


Why does that make it weakly acidic exactly??

Is it because the HNO₃ is a strong acid, therefore it won't steal the protons that are released from the NH₄ in solution?

 

[QuasiP]

You pretty much got it.

Nitric acid HNO3 is a strong acid, so it's conjugate base, NO3- is a very weak base. It will not affect the pH of the solution.

Ammonia NH3, on the other hand, is a moderately weak base, so it's conjugate acid NH4+ is a moderately strong acid. It will release protons in solution.

So, as you say, the NH4+ releases protons, the NO3- does not pick up protons, so the net effect is an acidic solution.