Answer:
Explanation:
According to Arrhenius Acid-Base Theory, acids are those substances that dissolved in water divide generating H⁺ together with an anion (ion with negative charge). In an aqueous solution, H⁺ protons immediately react with water molecules to form H₃O⁺ hydronium ions. A base, on the contrary, according to this theory, is a substance that liberates OH⁻ ions in aqueous solution.
This theory is valid only in aqueous medium.
You know: NH₃(g) + H₂O(l) → NH₄⁺(aq) + OH⁻(aq)
In this case, the water dissociates with the formation of hydrogen ions, H⁺, which NH₃ accepts to form the NH₄⁺ ion. So the water acts as an acid.
On the other hand, in reaction:
NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O(l)
NH₄⁺ dissociates with the formation of hydrogen ions, H⁺, which water accepts to form the H₃O⁺ ion. So NH₄⁺ acts as an acid.