Explain the following observations: (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic; (b) HF is called a weak acid, and yet it is very reactive; (c) although sulfuric acid is a strong electrolyte, an aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) contains more \(\mathrm{HSO}_{4}^{-}\) ions than \(\mathrm{SO}_{4}^{2-}\) ions.

NH3, also known as ammonia, is a weak base. When ammonia dissolves in water, it reacts with water molecules to form ammonium ions (NH4+) and hydroxide ions (OH-). The reaction can be written as: \( NH_3 (aq) + H_2O (l) \rightleftharpoons NH_4^+ (aq) + OH^- (aq) \) Though NH3 does not contain OH- ions itself, its aqueous solutions are still basic due to the formation of OH- ions during this reaction. The concentration of OH- ions determines the basicity of the solution.

Hydrogen fluoride (HF) is called a weak acid because it doesn't ionize completely in water, meaning that not all HF molecules dissociate into hydrogen ions (H+) and fluoride ions (F-) in an aqueous solution. The dissociation reaction is given by: \( HF (aq) \rightleftharpoons H^+ (aq) + F^- (aq) \) However, HF is reactive due to its high polarity and strong hydrogen bonding. The reactivity of HF can be attributed to its strong hydrogen-fluorine bond, and the high electronegativity of fluorine, which not only makes the HF bond highly polar but also allows for H+ to be easily accepted by other reactants in a given reaction.

Sulfuric acid, H2SO4, is a strong acid and a strong electrolyte, meaning it completely dissociates into its constituent ions in aqueous solutions. However, sulfuric acid is also a diprotic acid, which means it can donate two protons (H+) in a two-step process. The two dissociation reactions are as follows: 1) \( H_2SO_4(aq) \rightarrow H^+(aq) + HSO_4^-(aq) \) 2) \( HSO_4^-(aq) \rightleftharpoons H^+(aq) + SO_4^{2-}(aq) \) The first dissociation step is complete, while the second one is only partial. So, there is more HSO4- ion formed and less dissociation occurs in the second step, because the complete dissociation of H2SO4 into two H+ ions and SO42- ions is less favorable than the intermediate step, which produces HSO4- ions. As a result, an aqueous H2SO4 solution will contain more HSO4- ions than SO42- ions.