What happens when a weak base such as NH₃ is dissolved in water?

Verified step by step guidance

1. Identify the weak base in the problem, which is ammonia (NH₃).
2. Understand that when a weak base like NH₃ is dissolved in water, it partially ionizes. This means it does not completely dissociate into ions.
3. Write the chemical equation for the reaction of NH₃ with water: \[ \text{NH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4^+ + \text{OH}^- \]
4. Recognize that the equilibrium established in this reaction involves the formation of ammonium ions (NH₄⁺) and hydroxide ions (OH⁻), which makes the solution slightly basic.
5. Consider the concept of equilibrium and the fact that the position of equilibrium for a weak base like NH₃ lies far to the left, indicating that only a small fraction of NH₃ molecules are ionized at any given time.

Key Concepts

Weak Bases

Weak bases are substances that partially ionize in solution, meaning they do not completely dissociate into ions. Ammonia (NH₃) is a common example, which reacts with water to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻). This partial ionization results in a lower pH compared to strong bases, which fully dissociate.

Equilibrium in Chemical Reactions

When a weak base like NH₃ is dissolved in water, it establishes an equilibrium between the undissociated base and the ions produced. This dynamic balance is described by the equilibrium constant (K_b), which quantifies the extent of ionization. Understanding this concept is crucial for predicting the behavior of weak bases in solution.

pH and Basicity

The pH scale measures the acidity or basicity of a solution, with values below 7 indicating acidity and above 7 indicating basicity. When NH₃ dissolves in water, it increases the concentration of hydroxide ions, leading to a higher pH. This basic nature is a key characteristic of weak bases and is essential for understanding their effects in aqueous solutions.