Identify the acids and bases in each of the following reactions. 1. CN- + H2O ⇌ HCN + OH- 2. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) 3. NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
Identify the acids and bases in each of the following reactions.
- CN- + H2O ⇌ HCN + OH-
- HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq)
- NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
The Correct Answer and Explanation is:
Identifying Acids and Bases in the Reactions
Reaction 1:
CN−+H2O⇌HCN+OH−\text{CN}^- + \text{H}_2\text{O} \rightleftharpoons \text{HCN} + \text{OH}^-
- Base: CN⁻ (accepts a proton from H₂O)
- Acid: H₂O (donates a proton to CN⁻)
- Conjugate Acid: HCN
- Conjugate Base: OH⁻
Reaction 2:
HNO2(aq)+H2O(l)⇌NO2−(aq)+H3O+(aq)\text{HNO}_2(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{NO}_2^-(aq) + \text{H}_3\text{O}^+(aq)
- Acid: HNO₂ (donates a proton to H₂O)
- Base: H₂O (accepts a proton)
- Conjugate Base: NO₂⁻
- Conjugate Acid: H₃O⁺
Reaction 3:
NH3(aq)+H2O(l)⇌NH4+(aq)+OH−(aq)\text{NH}_3(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{NH}_4^+(aq) + \text{OH}^-(aq)
- Base: NH₃ (accepts a proton from H₂O)
- Acid: H₂O (donates a proton)
- Conjugate Acid: NH₄⁺
- Conjugate Base: OH⁻
Explanation
These reactions are examples of Brønsted-Lowry acid-base theory, which defines acids as proton (H⁺) donors and bases as proton acceptors.
In Reaction 1, the cyanide ion (CN⁻) accepts a proton from water, forming hydrogen cyanide (HCN) and hydroxide ion (OH⁻). Here, CN⁻ acts as a base and H₂O acts as an acid. The products show the conjugate acid-base pair: HCN (conjugate acid of CN⁻) and OH⁻ (conjugate base of H₂O). This reaction shows that CN⁻ is a weak base.
Reaction 2 shows nitrous acid (HNO₂) donating a proton to water, forming nitrite (NO₂⁻) and the hydronium ion (H₃O⁺). HNO₂ is the acid and H₂O is the base. The resulting species—NO₂⁻ and H₃O⁺—are the conjugate base and conjugate acid, respectively. This reaction is typical of a weak acid dissolving in water.
In Reaction 3, ammonia (NH₃) accepts a proton from water, resulting in ammonium ion (NH₄⁺) and hydroxide ion (OH⁻). NH₃ acts as a base, and H₂O is the acid. NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of water. This demonstrates NH₃’s property as a weak base.
Each of these reactions is an equilibrium, indicating that the acid and base are weak—they don’t completely dissociate or react in water. Understanding these acid-base pairs helps predict the direction of reactions and the pH of solutions, which is essential in chemistry, biology, and environmental science.
