Solution Composition

1
Solution Composition

• A solution is a mixture
• A mixture can have variable composition
• specify relative amounts of each substance
• dilute and concentrated is not specific enough

2
Solution Composition

• MOLARITY
• Molarity
• M
• moles of solute/liter of solution
• (Hintwatch for that liter of SOLUTION)
• the solution, remember, is made up of the solute
  plus the solvent
• Remember, the mass of solute cannot be added to a
  volume to determine the volume of the solution
• Volumes are not additive

3
Solution Composition

• Mass Percent
• Mass Percent mass of solute x 100
• mass of solution
• HINT again, watch for that mass of solution.
• The mass of solute can be added to the mass of
  solvent to get the mass of solution. You might
  need the density to convert from volume to mass!

4
Solution Composition

• Mole Fraction
• ca moles a/(moles a moles b .)
• ca na/(na nb )

5
Solution Composition

• Molality
• m moles of solute
• kg of solvent
• Hint note that this time, were talking about
  just the solvent!
• If the solution is very dilute, then the molality
  is very very close to the molarity.

6
Solution Composition

• Normality
• N equivalents
• liter of solution
• equivalents depend on the type of reaction
• Acid-Base Reaction 1 equivalent is the mass of
  acid or base that supplies ore accepts 1 mole of
  H
• The equivalent mass of H2SO4 is 49 g/mole, I.e.
  the mass of H2SO4 that supplies 1 mole of H
• 1 M H2SO4 is the same as 2 N H2SO4
• 1 M H2SO4 provides 2 moles H per liter of
  solution, I.e., 2 equivalents of H, therefore,
  it is 2 N H2SO4
• Normality Molarity x equivalents
• Normality Molarity x H (for acids or bases)

7
Solution Composition

• Normality
• For Redox reactions, the equivalent is the
  quantity of oxidizing or reducing agent that can
  accept or furnish 1 mole of electrons
• Normality Molarity x electrons
• 1 M MnO4- 5 N MnO4-
• 5 e- 8 H MnO4- gt Mn2 4 H2O

8
Energies of Solution Formation

• Solubility
• LIKE DISSOLVES LIKE
• polar solvents dissolve polar or ionic solutes
• nonpolar solvents dissolve nonpolar solutes

9
Energies of Solution Formation

• For something to dissolve
• Solute must be broken up into individual
  components (ions, molecules, atoms) (requires
  energy)
• Solvent must overcome IMFs between solvent
• particles (requires energy) to make room for
  solute particles
• Solvent interacts with solute (energy is
  released)

10
Energies of Solution Formation

• Enthalpy of solution (DHsoln)
• DHsoln DH1 DH2 DH3
• DHsoln lt 0, exothermic, favorable
• DHsoln gt 0, endothemic, not very favorable

11
Energies of Solution Formation

• Oil Spill
• Oil is nonpolar, only LDF between molecules,
  expect DH1 to be very small (but positive)
  because it doesnt take much energy to break weak
  LDF.
• DH2 will be large because it will take a lot of
  energy break H-bonds between water molecules to
  allow oil molecules in between
• DH3 will be small because nonpolar solute and
  polar solvent molecules do not interact.
• DHsoln will be large and positive, unfavorable
  for solution formation.

12
Energies of Solution Formation

• Dissolving sodium chloride in water
• DH1is large and positive because strong ionic
  forces must be broken between Na and Cl-
• DH2 is large and positive because it is difficult
  to break H-bonds between water molecules
• DH3 is large and negative because of the very
  favorable interaction between the ions and water
  molecules.
• DHsoln happens to be 3 kJ/mole, small, and
  positive, yet dissolving NaCl is favorable due
  to.ENTROPY INCREASE!!!

13
Energies of Solution Formation

• The moral of the story is
• Processes that require a large amount of energy
  (large and positive DH soln ) dont happen.
• A process with a small and positive DH soln can
  happen if entropy, or disorder, increases.

14
Factors affecting Solubility

• Polarity (like dissolves like)
• Ex fat soluble (hydrophobic - water fearing)
  vitamins, like Vitamin A, D, E, and K) can build
  up in the fatty tissues of the body.
  (Hypervitaminosis - the build up of excessive
  amounts of these vitamins )
• Ex water soluble (hydrophilic - water loving)
  vitamins, like Vitamin B and C, are not stored in
  the body, and needed to be constantly replenished.

15
Factors Affecting Solubility

• Pressure effects
• no effect on solubilities of liquids and solids
• pressure will increase the solubility of gases
• Carbonated beverages - CO2 is dissolved in
  solution under high pressure at the bottling
  plant. Open a can, release the pressure above
  the solution, and CO2 will rush out of solution.

16
Factors Affecting Solubility

• Henrys Law
• P kC
• Relationship between gas pressure and the
  concentration of dissolved gas
• P partial pressure of the gaseous solute above
  the solution
• C is the concentration of the dissolved gas
• k is a constant which depends on the particular
  solution
• Henrys law is obeyed for dilute solutions of
  gases that do not dissociate (O2, but not HCl)

17
Factors Affecting Solubility

• Temperature Effects
• Solubility does not always increase as
  temperature increases!
• The rate of solids dissolving will increase at
  higher temperature, but not necessarily the
  solubility.
• See graph of temperature dependence of
  solubilitybased on experimentsthe only way to
  know for sure!

18
Factors Affecting Solubility

• Solubility of gases decrease as temperature
  increases
• Environmental impact
• Thermal pollution - In industry, factories may be
  located near rivers, lakes, or oceans in order to
  take advantage of water for cooling. Warm water
  may be returned to the environment, resulting in
  a decrease in the oxygen concentration, which is
  hazardous to aquatic life.