Overview
This article explains why water is an excellent solvent, detailing how its molecular structure allows it to dissolve many substances vital for life, especially ions and polar molecules.
Water as a Solvent
- A solvent is a substance that dissolves other molecules (solutes) to form a solution.
- Water is called the "universal solvent" because it dissolves many types of molecules.
- Most of life's chemical reactions occur in aqueous (water-based) solutions.
Polarity and Dissolving Ability
- Water is a polar molecule with partial positive (hydrogen) and partial negative (oxygen) charges.
- Water's polarity allows it to form hydrogen bonds and electrostatic interactions with ions and other polar molecules.
- Polar substances and ions dissolve well in water; nonpolar substances (like oils) do not.
Hydration Shells and Dissociation
- Water molecules surround dissolved ions, forming hydration shells that keep ions dispersed in solution.
- In salt (NaCl), water breaks the ionic bonds, causing Na+ and Cl− ions to separate and disperse.
- Hydration shells result when water's partial charges attract oppositely charged solute ions.
Limitations and Nonpolar Molecules
- Nonpolar molecules lack charged regions and thus do not form hydration shells or dissolve in water.
- Nonpolar substances usually separate from water, forming layers or droplets.
Key Terms & Definitions
- Solvent — Substance that dissolves other substances to form a solution.
- Solute — Substance that is dissolved in a solvent.
- Solution — Homogeneous mixture of solute(s) and solvent.
- Aqueous Solution — Solution where water is the solvent.
- Polarity — Distribution of electrical charge leading to partial positive and negative regions in a molecule.
- Hydrogen Bond — Weak attraction between a hydrogen atom and an electronegative atom (like oxygen).
- Hydration Shell — Layer of water molecules surrounding a dissolved ion or molecule.
- Dissociation — Process where ionic compounds split into ions in solution.
- Nonpolar — Lacking regions of partial charge; does not interact well with water.
Action Items / Next Steps
- Review the differences between polar and nonpolar molecules.
- Practice identifying solutes that will or will not dissolve in water.
- Study the process of hydration shell formation for common ionic compounds.