Solutions

Solutions

1. Difference between a solution and a mixture

   • A solution is a homogenous mixture
     • Homogenous = the same throughout
   • A mixture is any combination of materials that are not chemically bonded.
   • Compound are therefore not mixtures or solutions.

2. If one substance can dissolve in another, the 2 substances are said to be miscible.

3. Types of substances

   • Solid in a liquid
     • Sugar (solute) in tea (solvent)
   • Gas in a gas
     • Air, in which N2 is the solvent and O2 is the solute
   • Solid in a solid
     • Steel alloy, in which iron is the solvent and carbon is the solute
   • Liquid in a liquid
     • Antifreeze (water is the solvent, ethylene glycol the solute)
   • Gas in a liquid
     • Soda (water is the solvent, CO2 is the solute)
   • Liquid in a solid
     • Dental amalgam (silver is the solvent, mercury the solute)

4. Solvation in Aqueous Solutions

   • Solute particles must separate and the solute and solvent particles must mix.
   • If the attractive forces between the solvent and solute are greater than the attractive forces holding the solute particles togethr, the surrounded solute particles then move away from the solid solute out into the solution.
     • If the attractive forces holding the particles of the solid together are greater than the attractive forces between the solvent and the solid, the solid particles stay together, i.e. do not dissolve
   • The process of surrounding solute particles with solvent particles to form a solution is called solvation.

5. Electonegativity

   • Refers to the ability of an atom to draw electrons to it.
   • Fluoride = most electronegative element (3.98) Francium = least electronegative element (0.7)
   • In a chemical bond, if the difference in electronegativities is:
     • >1.7 = ionic bond
     • 0.4-1.7 = uneven sharing (polar covalent)
     • 0-0.4 = even sharing (nonpolar covalent)
   • Water is a polar molecule
     • The electrons are shared unevenly
     • The oxygen side is "partially negative" and the hydrogen side is "partially positive"
     • The polar nature of water enables it to dissolve many compounds
     • Ions in aqueous solution surrounded by water molecules are called hydrated ions

6. Polar Covalent Solvation

   • A polar solute like sucrose can dissolve in a polar solvent like water.
     • The partially positive parts of sucrose are more attracted to the partially negative parts of the water molecule than each other
   • LIKE DISSOLVES LIKE.
     • Nonpolar solvents can dissolve nonpolar solutes
     • Nonpolar solvents cannot dissolve polar solutes
     • Polar solvents can dissolve polar solutes
   • A solution of a covalent compound is different from a solution of an ionic compound because:
     • The ionic compound breaks into inidividual ions (eg NaCl and water)
     • The covalent molecule stays together, covalent bonds don't break (eg sucrose and water)

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