NH3 is: A. a strong acid B. a strong base C. a weak acid D. a weak base
The correct answer and explanation is:
Correct Answer: D. a weak base
Ammonia, represented by the chemical formula NH₃, is classified as a weak base. In aqueous solutions, ammonia reacts with water to a limited extent, forming ammonium ions (NH₄⁺) and hydroxide ions (OH⁻). The reaction is as follows:
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻
This equilibrium reaction does not go to completion. Instead, only a small fraction of ammonia molecules accept protons from water, which means that the concentration of hydroxide ions produced is relatively low. Because of this partial ionization, ammonia is categorized as a weak base.
A strong base, like sodium hydroxide (NaOH), dissociates completely in water, releasing a high concentration of hydroxide ions. Ammonia does not behave like this. Its basicity is due to the lone pair of electrons on the nitrogen atom, which allows it to accept a proton from water molecules, forming the ammonium ion. However, because this proton acceptance is not complete and reversible, the base is considered weak.
The strength of a base is often measured by its base dissociation constant (Kb). For ammonia, the Kb value is approximately 1.8 × 10⁻⁵, which is much lower than that of strong bases. This value confirms that ammonia does not produce a large amount of OH⁻ in solution.
Despite being a weak base, ammonia is commonly used in household cleaners and fertilizers due to its effectiveness in reacting with acids and breaking down grease or stains. Understanding that NH₃ is a weak base is important in chemistry, especially in acid-base reactions, buffer systems, and pH calculations.