How does ammonia behave as a Bronsted base: #"(i) "NH_3(g) + 7/2O_2(g) rarr 2NO_2(g) + 3H_2O# #"(ii) "2NH_3(g) rarr NH_4^+ +NH_2^(-) # #"(iii) "NH_3(g) + H_3CBr(g) rarr H_3CBr(g) + HBr(g)# #"(iv) "NH_3(aq) +H_2O(l) rarr NH_4^+ + HO^-#?

1 Answer
Dec 4, 2015

Answer:

The acid base reaction (the last one!).

Explanation:

Ammonia is a Bronsted base:

#NH_3(aq) + H_2O(l) rightleftharpoons NH_4^+ + OH^-# #pK_b = 4.75#

I am not going to solve this equation using #pK_b#, but most of the ammonia is present as #NH_3#, the free base.

For AS/A2 level; ammonia is a very water like solvent. In pure ammonia another acid/base equilibrium operates, that is comparable to the #H_3O^+; OH^-# equilibrium in water.

#2NH_3(l) rightleftharpoons NH_2^(-) + NH_4^+#

THIS ONLY OPERATES IN LIQUID AMMONIA; IT DOES NOT OPERATE IN WATER. The amide ion, #NH_2^-#, does not exist in water.