The pKb of urea is 13.9. This value signifies its basicity in aqueous solutions.
Understanding Urea's Basicity
The pKb (the negative logarithm of the base dissociation constant, Kb) quantifies the strength of a base. A higher pKb value indicates that a substance is a weaker base, meaning it has a limited tendency to accept protons (H+) when dissolved in water.
With a pKb of 13.9, urea is characterized as a very weak base. Its chemical structure, which includes two amine groups, might initially suggest some basicity. However, the strong electron-withdrawing effect of the adjacent carbonyl group (C=O) significantly reduces the electron density on the nitrogen atoms. This reduction in electron density makes the nitrogen atoms less available to accept protons, thus diminishing urea's basicity. Consequently, uronium, the conjugate acid of urea, is considered a relatively strong acid when compared to the conjugate acids of stronger bases.
Key Properties of Urea
Urea is a widely used organic compound with diverse applications across multiple industries and biological systems. Understanding its fundamental properties, including its basicity and solubility, is crucial for its various uses.
| Property | Value |
|---|---|
| Basicity (pKb) | 13.9 |
| Conjugate Acid | Uronium |
| Solubility in water | 545 g/L (at 25 °C) |
| Solubility in glycerol | 500 g/L |
| Solubility in ethanol | 50 g/L |
| Solubility in acetonitrile | ~4 g/L |
Applications and Significance
The weak basicity and high water solubility of urea make it invaluable in several sectors:
- Agriculture: It serves as a cornerstone in nitrogen fertilizers, providing a stable and efficient source of nitrogen essential for plant growth.
- Medicine: In dermatology, urea is used for its hydrating and exfoliating properties. It also finds use in certain diagnostic procedures.
- Industry: Urea is a key raw material in the manufacturing of plastics, particularly urea-formaldehyde resins, as well as adhesives and other industrial chemicals.
Its characteristic weak basicity ensures that urea largely remains in its neutral form in most aqueous environments, contributing to its stability and broad utility.
