Predict whether aqueous solutions of the following compounds are acidic, basic, or neutral: (a) \(\mathrm{NH}_{4} \mathrm{Br}\), (b) \(\mathrm{FeCl}_{3},(\mathrm{c})\) \(\mathrm{Na}_{2} \mathrm{CO}_{3},\) (d) \(\mathrm{KClO}_{4},\) (e) \(\mathrm{NaHC}_{2} \mathrm{O}_{4}\)

When ammonia (\(\mathrm{NH}_{4}\)), a weak base, is mixed with hydrobromic acid (\(\mathrm{HBr}\)), a strong acid, it forms the salt \(\mathrm{NH}_{4}\mathrm{Br}\). When this compound is dissolved in water, it dissociates into ammonium (\(\mathrm{NH}_{4}^{+}\)) and bromide (\(\mathrm{Br}^-\)) ions. The ammonium ion can further react with water to give hydronium ions and ammonia. This will increase the hydronium ion concentration, making the solution acidic. \[NH_{4}^{+}(aq) + H_2O(l) \rightleftharpoons NH_{3}(aq) + H_{3}O^{+}(aq)\]

When ferric chloride (\(\mathrm{FeCl}_{3}\)) is dissolved in water, it will dissociate into ferric (\(\mathrm{Fe}^{3+}\)) and chloride ions (\(\mathrm{Cl}^-\)). The \(\mathrm{Fe}^{3+}\) ions will react with the water molecules to form hydrated ions, releasing hydronium ions (H₃O⁺), which will increase the H₃O⁺ ion concentration, making the solution acidic. \[Fe^{3+}(aq) + 6H_2O(l) \rightleftharpoons [Fe(H_2O)_{6}]^{3+}(aq) \rightleftharpoons [Fe(H_2O)_{5}(OH)]^{2+}(aq) + H_{3}O^{+}(aq)\]

When sodium carbonate (\(\mathrm{Na}_{2}\mathrm{CO}_{3}\)) is dissolved in water, it will dissociate into two sodium ions (\(\mathrm{Na}^{+}\)) and one carbonate ion (\(\mathrm{CO}_{3}^{2-}\)). The sodium ions have no significant interaction with water molecules, but the carbonate ions will react with water molecules to form bicarbonate (\(\mathrm{HCO}_{3}^-\)) and hydroxide (\(\mathrm{OH}^-\)) ions. \[CO_{3}^{2-}(aq) + H_2O(l) \rightleftharpoons HCO_{3}^{-}(aq) + OH^{-}(aq)\] The presence of hydroxide ions makes the solution basic.

When potassium perchlorate (\(\mathrm{KClO}_{4}\)) is dissolved in water, it dissociates into potassium (\(\mathrm{K}^{+}\)) and perchlorate (\(\mathrm{ClO}_{4}^-\)) ions. Both potassium and perchlorate ions are weak conjugate ions and don't participate in significant equilibrium reactions with water. Therefore, their concentrations won't affect the H₃O⁺ or OH⁻ concentrations, and the solution will remain neutral.

Sodium hydrogen tartrate (\(\mathrm{NaHC}_{2} \mathrm{O}_{4}\)) is the sodium salt of the weak acid, tartaric acid and can be considered the product of a neutralization reaction between a weak acid and a strong base. When dissolved in water, it dissociates into sodium (\(\mathrm{Na}^{+}\)) and hydrogen tartrate (\(\mathrm{HC}_{2}\mathrm{O}_4^-\)) ions. The sodium ions do not significantly interact with water, but hydrogen tartrate ions can participate in an equilibrium with water molecules: \[HC_{2}O_4^-(aq) + H_2O(l) \rightleftharpoons C_{2}O_{4}^{2-}(aq) + H_3O^{+}(aq)\] However, hydrogen tartrate ions have a weak acidic character and don't significantly influence the acidity or basicity of the solution. Therefore, the solution can be considered nearly neutral. In conclusion, (a) \(\mathrm{NH}_{4} \mathrm{Br}\) is acidic, (b) \(\mathrm{FeCl}_{3}\) is acidic, (c) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is basic, (d) \(\mathrm{KClO}_{4}\) is neutral, and (e) \(\mathrm{NaHC}_{2} \mathrm{O}_{4}\) is nearly neutral.