Solutions

1
Solutions

• Homogeneous Mixtures

2
Key Definitions

• Solute
• Dissolved particles in a solution
• The lesser component
• Solvent
• The dissolving medium in a solution
• The greater component
• Example Saline Solution for contact lenses
• Solute sodium chloride
• Solvent water

3
More definitions

• Miscible
• Liquids that will dissolve in each other
• Ex. Oil and gasoline for 2 stroke engines
• Immiscible
• 2 liquids that are insoluble in each other
• Ex. Oil and water

4
How much solute is dissolved?

• Saturated solution
• Contains the maximum amount of dissolved solute
• If you add more solute, it will fall to the
  bottom
• Unsaturated solution
• Contains less than the maximum amount of
  dissolved solute
• If you add more solute, it will dissolve

5
Relative Humidity

• A measure of how much water vapor is in the air,
  compared to maximum amount of water the air can
  hold at that temperature
• 100 humidity rain is possible!
• People feel most comfortable indoors when the
  relative humidity is between 40-60.

6
Supersaturated Solutions

• Sometimes solutions can be prepared that have
  MORE dissolved solute than a saturated solution
• Unstable!
• Often used in candy making processes
• Video clip

7
Solubility Diagrams

• Solubility information is often presented
  graphically

8
Interpreting Solubility Diagrams

• Most substance become more soluble as temperature
  increases.
• Gases typically become LESS soluble as
  temperature increases.
• Note the units on the y axis often given as
  grams of solute/100 g solvent.

9
To speed up the solution process

• Increase the surface area of the solute
• Which would dissolve faster a sugar cube or
  powdered sugar?
• Stir the solution
• Increase the temperature of the solution

10
Rule of thumb for solubility

• Like dissolves like
• Solutes tend to dissolve in solvents with similar
  properties.
• Nonpolar substances typically dissolve in
  nonpolar solvents.
• Ionic solids tend to dissolve in polar solvents.

11
Solution Concentrations

• Ratio of solute to solvent
• Concentrated high ratio of solute to solvent
• Dilute low solute/solvent ratio
• Several different ways to calculate
• Most common
• Molarity symbol M
• Percent solutions m/m, m/v, v/v
• Parts per million
• Molality

12
Molarity

• Definition
• Since mol g/gfm,

13
Percent Solutions

• Easy and reliable to calculate
• Mass/mass, mass/volume, volume/volume
• Frequently used in biology medicine

14
Molality

• Used to calculate changes in physical properties
  of solutions
• Note subtle differences from molarity formula!
• molal solutions

15
Vapor Pressure

• Particles at the surface of a liquid may
  evaporate or vaporize, if they have enough
  kinetic energy.
• If this happens in a sealed container, the
  particles of escaped liquid (now in the gas
  phase) will collide with the container walls and
  exert a vapor pressure above the liquid

16
Vapor Pressure Diagrams

• Vapor pressure data is often presented graphically

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Boiling Point

• Boiling
• when bubbles of gas form anywhere in the liquid
  and then rise to the surface
• Boiling point
• the temperature at which the vapor pressure of
  the liquid is just equal to the external pressure
• Normal boiling point
• the boiling point of a liquid at a pressure of
  101.3 kPa (1 atm)

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Colligative Properties

• Addition of a solute changes the properties of
  the system
• The solution will have different properties than
  the pure solvent
• Adding solute changes the freezing point, boiling
  point, vapor pressure
• These changes depend only on the number of
  particles added (NOT the identity of the
  particles)

19
Phase Diagrams
20
Phase Diagrams

• Closed system
• Triple Point
• Where solid, liquid, and gas can coexist
• Critical Point
• Above this point, gas and liquid are
  indistinguishable
• supercritical fluids

21
Colligative Properties

• Freezing Point Depression
• The solution will freeze at a lower temperature
  than the pure solvent
• Why we put salt on sidewalks during winter
• Antifreeze in cars
• Boiling Point Elevation
• The solution will boil at a higher temperature
  than the pure solvent
• Cool simulation

22
vant Hoff Factor (i)

• Some substances dissociate into ions, resulting
  in more solute particles dissolving
• vant Hoff Factor the theoretical (maximum)
  number of particles formed when a substance
  dissociates
• The real degree of ionization is typically
  slightly less than predicted by the vant Hoff
  factor

23
Predicting vant Hoff factors

• For all covalently bonded substances,
• i 1
• For ionic substances
• I number of ions present in formula
• Ex.
• NaCl i 2
• Al(NO3)3 i 4
• MgCl2 i 3

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Calculating Colligative Properties

• ?Tbp kbp?i?m where kbp is a constant for each
  solvent
• Calculate the new boiling point by adding ?Tbp to
  the boiling point of the pure solvent
• ?Tfp kfp?i?m where kfp is a constant for each
  solvent
• Calculate the new boiling point by subtracting
  ?Tbp from the freezing point of the pure solvent