Which of the following is a Bronsted-Lowry base but NOT an Arrhenius base? NaOH NH3 KOH HCI
The Correct Answer and Explanation is:
The correct answer is NH3 (Ammonia).
Explanation:
To understand why NH3 is a Bronsted-Lowry base but not an Arrhenius base, we first need to differentiate between the Arrhenius and Bronsted-Lowry definitions of acids and bases.
1. Arrhenius Definition:
- According to the Arrhenius definition, an Arrhenius base is a substance that dissociates in water to produce hydroxide ions (OH⁻).
- For example, NaOH, KOH, and even HCl, when dissolved in water, dissociate to release OH⁻ or H⁺ ions, respectively. NaOH dissociates to produce Na⁺ and OH⁻, and KOH dissociates to produce K⁺ and OH⁻.
2. Bronsted-Lowry Definition:
- According to the Bronsted-Lowry definition, a Bronsted-Lowry base is any substance that can accept a proton (H⁺).
- Ammonia (NH₃), for example, can accept a proton (H⁺) from water to form ammonium ions (NH₄⁺). The reaction looks like this: NH3+H2O→NH4++OH−NH_3 + H_2O \rightarrow NH_4^+ + OH^-NH3+H2O→NH4++OH−
- NH₃ does not produce OH⁻ directly by dissociation in water. Instead, it accepts a proton from water molecules, which in turn generates OH⁻, making NH₃ a Bronsted-Lowry base.
Why NH₃ is not an Arrhenius base:
- NH₃ does not directly release hydroxide ions (OH⁻) when dissolved in water. It accepts protons, which makes it a Bronsted-Lowry base, but it doesn’t fit the strict criteria for an Arrhenius base, which requires a substance to release OH⁻ ions directly.
In summary, while NH₃ is a Bronsted-Lowry base (because it accepts protons), it is not an Arrhenius base, as it does not directly produce hydroxide ions.
