1. Dissociation in Water:
When NaOH dissolves in water, it undergoes complete dissociation, meaning that all the sodium (Na+) and hydroxide (OH-) ions are separated. The dissociation equation is:
NaOH(aq) → Na+(aq) + OH-(aq)
In contrast, Ammonia undergoes incomplete dissociation in water. Only a small percentage of NH3 molecules react with water to form ammonium (NH4+) and hydroxide ions (OH-). The dissociation equation is:
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
The extent of dissociation, also known as the dissociation constant (Kb), is much lower for NH3 compared to NaOH. This means that NaOH produces a higher concentration of hydroxide ions in water, making it a stronger base.
2. Ionic Character:
Sodium hydroxide is an ionic compound, consisting of positively charged sodium ions (Na+) and negatively charged hydroxide ions (OH-). The strong electrostatic attraction between these oppositely charged ions stabilizes the compound. In contrast, Ammonia is a covalent molecule, where nitrogen and hydrogen atoms share electrons to form a stable structure.
3. Hydration Energy:
When hydroxide ions (OH-) are formed from NaOH, they are surrounded by water molecules, which release hydration energy. This energy released stabilizes the hydroxide ions, making them less likely to recombine with hydrogen ions (H+) and reform water molecules. On the other hand, the hydration energy of ammonium ions (NH4+) is lower, which means that NH3 does not benefit as much from this stabilizing effect.
4. Conjugate Acid Strength:
The strength of a base can also be understood in terms of its conjugate acid. The conjugate acid of a base is the species formed when the base accepts a proton. In the case of NaOH, the conjugate acid is water (H2O), which is a very weak acid. This means that NaOH is more effective in removing protons from other molecules, making it a stronger base. In contrast, the conjugate acid of NH3 is ammonium ion (NH4+), which is a stronger acid compared to water. This indicates that NH3 is less effective in removing protons, reducing its basicity.
In summary, Sodium hydroxide (NaOH) is a stronger base than Ammonia (NH3) because it undergoes more complete dissociation in water, has a higher ionic character, benefits more from hydration energy, and has a weaker conjugate acid. These factors contribute to NaOH being more effective in accepting protons and producing hydroxide ions, making it a stronger base.
