Ammonium salts + alkali --> Ammonia + H20 + salt?

Question

Since ammonia turns red litmus blue, it must have alkaline properties.

Hence, why are ammonium salts (which should also have alkaline properties since ammonia does) reactive with alkalis to product ammonia etc.

Answer 1

firstly, the definitions of acid and base/alkali are important for tis question. acid is a proton (H+) donor. base is a proton acceptor. alkali is a soluble type of base.
ammonia does have alkaline properties, because it accepts a proton to become a "salt": NH3 + H+ ------> NH4+ (ammonium ion). note that ammonium salts refer to compounds that have NH4+ as the positive half, while the negative half can be Cl, NO3 etc.

ammonium salts DO NOT act as alkali just because ammonia acts like one. in fact, ammonium acts like an acid, since it can donate the H+ to form back ammonia, NH3. especially when u add alkali, which almost always have OH- (NaOH, KOH). the combination of H+ and OH- to form water is extremely favorable (energetically, since water is very stable), thus, NH4+ will lose its H+ to become ammonia again! the salt is formed because the negative half of the ammonium salt will combine with the postive half of the alkali (Na+, K+). the equation is generally:
(NH4)X + YOH --------> NH3 + XY + H2O
for example, NH4Cl + NaOH -------> NH3 + NaCl + H2O

the ionic equation would then be (H+) + (OH-) ------> H2O, which represents a neutralisation process.

Answer 2

Because in this case, the ammonium salts are the base.