Unit 7

Solutions

  • Solutions are homogeneous mixtures that are stable

  • They are formed through a physical process

  • They are composed of solutes (the material being dissolved) and the solvent (the dissolving medium)

  • Solvents are usually in greater quantity than solutes

  • possible combinations: solid/solid (alloys- brass, bronze), liquid/liquid (ethanol and h20), gas/gas (air), gas/liquid (river water, 02 in h20, carbonated water), solid/liquid (saline, kool-aid)

  • “Like dissolves like”

  • non-polar solute with a non-polar solvent (same change all the way)

  • ionic/polar solute and a polar solvent

Calculations

  • Molarity = moles solute/liter solution

  • temperature dependent (at the same temp it was mixed at)

  • ex: 2.498 mols NaCl dissolved in 16.148 L of the solution (solvent + solute), .1547 M

  • Molality (m) = moles solute/kg solvent

  • temperature independent based on colligative properties (depends on number of particles)

  • ex: 2.498 mols of NaCl and 16000 g H20, .1561 m

  • mole fraction (mole %)

  • mol a/mol a + mol b

  • ex: 2.00 mols NaCl/2.00 mols NaCl + 5.00 mols H20 = .286

  • % by mass = g solute/g solution x 100

  • % by volume = volume of solute/volume of solution x 100

Colligative Properties

  • Physical properties of solutions that are affected by the number of solute particles but not by their indentity of the solute particles are called colligative properties

  • These include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure

  • The more ions that form from the dissociation of an ionic solid, results in a greater effect

  • A reaction that results in a yield of 5 particles will have a greater impact than a reaction with a 2 particle yield

  • nonionic (covalent) substances that dissolve dissociate as whole molecules, so 1 mole of glueclose only yields one mole of particles (nonvolatile, non-electrolyte)

  • i = von hoffs

  • The changes in boiling point and freezing point can be projected by knowing the molality (m) of the solution and the associated constant from a given table

  • change in freezing point = iKfm where i is the number of ions

  • change in boiling point = ikbm