The solubility of p-nitrophenol in water is 1.7 grams per 100 grams of water.
Understanding Solubility
Solubility describes the maximum amount of a substance (the solute) that can dissolve in a given amount of a solvent at a specific temperature, forming a homogeneous solution. For p-nitrophenol, this value indicates how much of the compound can be dissolved and evenly dispersed in water.
Solubility of Nitrophenol Isomers in Water
To provide a comprehensive understanding, it's insightful to compare the solubility of p-nitrophenol with its isomer, o-nitrophenol:
| Compound | Solubility (g/100 g H₂O) |
|---|---|
| o-nitrophenol | 0.2 |
| p-nitrophenol | 1.7 |
As evident from the table, p-nitrophenol exhibits significantly higher solubility in water compared to its ortho-isomer. This substantial difference is a key illustration of how molecular structure critically influences a compound's physical properties, especially its interactions with a polar solvent like water.
Factors Influencing P-Nitrophenol's Solubility
The striking difference in water solubility between ortho- and para-nitrophenol is primarily due to their respective abilities to form hydrogen bonds:
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P-Nitrophenol's Enhanced Solubility: In p-nitrophenol, the hydroxyl (-OH) group and the nitro (-NO₂) group are positioned para (opposite) to each other on the benzene ring. This spatial arrangement prevents the formation of intramolecular hydrogen bonds, meaning hydrogen bonds within the same molecule. Consequently, both the hydroxyl group and the nitro group are readily available to form strong intermolecular hydrogen bonds with surrounding water molecules. The extensive network of hydrogen bonds formed between p-nitrophenol molecules and water molecules significantly increases its affinity for water, leading to its high solubility.
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O-Nitrophenol's Lower Solubility: Conversely, in o-nitrophenol, the hydroxyl and nitro groups are located adjacent to each other on the benzene ring. This close proximity allows for the formation of a strong intramolecular hydrogen bond between the hydrogen atom of the -OH group and an oxygen atom of the -NO₂ group within the same molecule. This internal hydrogen bonding effectively "ties up" the groups that would otherwise interact with water. By forming these internal bonds, o-nitrophenol molecules become less available to form hydrogen bonds with water molecules, thus reducing their interaction with the solvent and resulting in much lower water solubility.
This distinction underscores the critical role of hydrogen bonding and specific molecular geometry in determining how soluble an organic compound will be in water.
Practical Implications
Understanding the solubility characteristics of compounds like p-nitrophenol is vital across various scientific and industrial applications:
- Chemical Synthesis and Purification: Solubility data guides chemists in selecting appropriate solvents for reactions, crystallizations, and other purification processes.
- Environmental Science: It helps predict the environmental fate and transport of chemicals, influencing their mobility in soil and water systems.
- Pharmaceutical Development: In drug formulation, solubility is a crucial factor for drug absorption, distribution, and overall bioavailability in the human body.
The higher water solubility of p-nitrophenol makes it a more amenable compound for aqueous-based applications compared to its less soluble isomer.
