Write equations which represent the dissociation of each of these acids or bases in aqueous solution. Use a single arrow in the case of a strong acid or base, and a double arrow to represent the equilibrium condition that exists in the solution of a weak acid or base. a) KOH b) HClO4 c) HCN d) C6H5NH2 (a weak base)
The correct answer and explanation is:
Dissociation Equations:
- KOH (Strong Base)
Equation: KOH(aq)→K+(aq)+OH−(aq)\text{KOH} (aq) \rightarrow \text{K}^+ (aq) + \text{OH}^- (aq) Explanation: Potassium hydroxide (KOH) is a strong base, meaning it dissociates completely in aqueous solution. The potassium ion (K⁺) and hydroxide ion (OH⁻) are produced in a 1:1 ratio. - HClO₄ (Strong Acid)
Equation: HClO4(aq)→H+(aq)+ClO4−(aq)\text{HClO}_4 (aq) \rightarrow \text{H}^+ (aq) + \text{ClO}_4^- (aq) Explanation: Perchloric acid (HClO₄) is a strong acid and dissociates completely in water, releasing hydrogen ions (H⁺) and perchlorate ions (ClO₄⁻). The dissociation happens without equilibrium, meaning no reversible reaction occurs. - HCN (Weak Acid)
Equation: HCN(aq)⇌H+(aq)+CN−(aq)\text{HCN} (aq) \rightleftharpoons \text{H}^+ (aq) + \text{CN}^- (aq) Explanation: Hydrocyanic acid (HCN) is a weak acid, meaning it only partially dissociates in aqueous solution. The reaction reaches an equilibrium where both HCN and its dissociation products (H⁺ and CN⁻) exist in the solution. - C₆H₅NH₂ (Weak Base)
Equation: C6H5NH2(aq)+H2O(l)⇌C6H5NH3+(aq)+OH−(aq)\text{C}_6\text{H}_5\text{NH}_2 (aq) + \text{H}_2\text{O} (l) \rightleftharpoons \text{C}_6\text{H}_5\text{NH}_3^+ (aq) + \text{OH}^- (aq) Explanation: Aniline (C₆H₅NH₂) is a weak base, so it reacts partially with water. The reaction is reversible, producing aniline hydrochloride (C₆H₅NH₃⁺) and hydroxide ions (OH⁻), and the system reaches an equilibrium.
Summary:
- Strong acids and bases like HClO₄ and KOH dissociate completely in solution, represented by a single arrow.
- Weak acids and bases like HCN and C₆H₅NH₂ dissociate partially, represented by a double arrow to indicate equilibrium. The concentration of the undissociated acid or base remains significant, and the products are in equilibrium with each other.