Organic solvents work primarily by disrupting the intermolecular forces holding a solute together, allowing the solute to disperse among the solvent molecules. In essence, they dissolve or disperse other substances due to their chemical properties and interactions.
Here's a breakdown of how they function:
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Solubility Principles: "Like Dissolves Like" The fundamental principle is that solvents tend to dissolve solutes with similar polarity.
- Polar solvents, such as water and alcohols (e.g., ethanol), effectively dissolve polar solutes, like salts and sugars. This is because they can form strong intermolecular interactions like hydrogen bonds or dipole-dipole interactions with the solute molecules.
- Non-polar solvents, such as hexane, toluene, and diethyl ether, dissolve non-polar solutes like fats, oils, and waxes. This is due to London dispersion forces that exist between non-polar molecules.
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Disrupting Intermolecular Forces:
- Organic solvents work by weakening or overcoming the forces holding the solute molecules together. For example, in a crystalline solid, the molecules are held together by strong intermolecular forces. The solvent molecules insert themselves between the solute molecules, disrupting these forces and allowing the solute to disperse.
- Polar solvents can solvate ions by surrounding them with solvent molecules, stabilizing the ions in solution and preventing them from reassociating into a solid lattice.
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Types of Organic Solvents and their Mechanisms:
Solvent Type Polarity Examples Mechanism of Action Aliphatic Hydrocarbons Non-polar Hexane, Pentane Dissolve non-polar substances via London dispersion forces. Aromatic Hydrocarbons Non-polar Toluene, Benzene Dissolve non-polar substances; pi-pi stacking interactions can also play a role. Halogenated Hydrocarbons Polar Chloroform, DCM Dissolve a range of substances due to induced dipole-dipole interactions. Alcohols Polar Ethanol, Methanol Dissolve polar substances via hydrogen bonding and dipole-dipole interactions. Glycols and Glycol Ethers Polar Ethylene Glycol Excellent solvents for polar and some non-polar substances due to dual functionalities. -
Dispersion vs. Dissolution: It's important to note that "dissolving" implies a true solution at the molecular level. Organic solvents can also "disperse" substances, meaning they create a mixture where the solute particles are finely distributed throughout the solvent but are not necessarily molecularly dissolved. This can occur with larger particles or polymers.
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Volatility: Organic solvents are typically volatile, meaning they evaporate easily at room temperature. This property is essential for many applications, such as in paints, coatings, and cleaning products, where the solvent needs to evaporate after application, leaving behind the solute (e.g., the paint pigment).
In summary, organic solvents facilitate the dissolution or dispersion of other substances by weakening the intermolecular forces holding those substances together, allowing them to intermix with the solvent at a molecular level. The effectiveness of a solvent depends on its polarity relative to the solute, with "like dissolving like" being the governing principle.
