CHAPTER 13
Mixtures and Concentrations
Types of Mixtures
• Solutions
• Suspensions
• Colloids
Solutions
• Soluble
– Capable of being dissolved
• Solution
– Homogenous mixture – thoroughly
mixed
• Solvent
– Dissolving medium – “doing” the
dissolving
– Often Water = the universal solvent
• Solute
– Substance being dissolved
• Example – Sugar Water
Solutions
• Electrolyte
– Conducts electric current when in solution
– Example – NaCl – IONICS, Acids, Bases
• Nonelectrolyte
– Does NOT conduct electricity
– Example – Sugar – MOLECULAR
SUBSTANCES
Solutions
• Types of solutions
– Gas solutions
• Gas with gas – quickly intermingle – air
• Constant motion
– Liquid solutions
• Liquid with gas – Soda (CO2 in sugar water)
• Liquid with liquid – Vinegar (acetic acid + water)
– Solid solutions
• Alloy – two or more metals are mixed
– Sterling silver (Cu + Ag)
– Brass (Cu + Zn)
– Bronze (Cu + Sn)
Solutions
• Evidence that it is a solution
– Cannot be filtered
– NO light scattering
Suspensions
• Heterogeneous mixture with particles that
settle out
– Water particles are not strong enough to keep
other particles from settling out
– Example - Muddy water
• Evidence that it is a suspension
– Can be filtered
– Particles settle
– May scatter light
– Not transparent
Colloids
• In-between a solution and a suspension
– Medium size particles
– Small enough to be kept in “permanent”
suspension
• Dispersed phase
– Solute-like particles
• Dispersing phase
– Solvent-like particles
Colloids
• Evidence that it is a
colloid
– Scatters light
– Does not settle
• Tyndall Effect
– Light scattered by colloidal
particles
Examples – Jello; Cool
Whip
Time: 5:39-6:26
Making Solutions
• Factors affecting rate of dissolving – ways
to speed up dissolving
– Increase surface area of solute
• More solute touches solvent
• Ex – crush, spread out
– Agitate solution
• Spreads out already dissolved solute to bring in
more fresh solvent in contact with solute
• Ex – stir, shake
– Heat solvent
• Particles move faster as energy increases
• More collisions between solute and solvent
Solubility
• Solution equilibrium – opposing rates of
dissolving and crystallizing are equal
– Unsaturated
• Contains less than maximum amount of solute
– Saturated
• Contains maximum amount of solute
• More will NOT dissolve
– Supersaturated
• Has more solute than a saturated solution at same
conditions
Supersaturated solutions
• Steps to make
– Heat saturated solution
– Add more solute
– Cool slowly
– Addition of one more crystal?
• Will crystallize entire solution!!
• Video
Factors affecting solubility
• Solubility = Ability to dissolve
• Type of solute/solvent
– “like dissolves like”
– Immiscible – Liquids NOT soluble in each
other
• Water and oil
– Miscible – Liquids are soluble in each other
• Vinegar
Factors affecting solubility
• Pressure
– Increase pressure = increase amount of gas
dissolved
– Example – Soda
– Henry’s Law
• Increase pressure = Increase solubility of a gas
Factors affecting solubility
• Temperature
– If solute is gas
• Increase temp = Decrease solubility
– If solute is solid usually…
• Increase temp = Increase solubility
Heat of Solution
• Amount of energy released/absorbed
when solute dissolves in solvent (kJ/mol)
– Endothermic
• Absorbs heat
• Positive (+) heat of solution
– Exothermic
• Releases heat
• Negative (-) heat of solution
– Solvated – solute particles surrounded by
solvent
Bond changes during solution
formation
• Solute-solute attractions broken
– REQUIRES ENERGY
• Solvent-solvent attractions broken
– REQUIRES ENERGY
• Solute-solvent attractions formed
– RELEASES ENERGY
Compare energies
• Process is ENDOTHERMIC if:
– Steps 1 + 2 > Step 3
• Process is EXOTHERMIC if:
– Step 3 > Steps 1 + 2
Concentrations
• Percent by Mass
• Mole Fraction (needs to be added)
• Molarity (M)
• Molality (m)
Percent by mass
• % Mass = Mass solute x 100%
Mass total solution
Solution = solute + solvent !!!!
Examples
Mole Fraction
• Mole Fraction (X) = Moles substance A
Total moles solution
Examples
Molarity
• Molarity (M) = Moles solute
Liters solution
Examples
Molality
• Molality (m) = Moles solute
kg solvent
Examples
Colligative Properties
• A property that depends of number of
solute particles
– Vapor-Pressure Lowering
– Boiling Point Elevation
– Freezing Point Depression
• Nonvolatile – a substance that does NOT
evaporate very much
Vapor-Pressure Lowering
• Adding a nonvolatile substance lowers the
vapor pressure
– Increase solute = Decrease VP
• SIMPLIFIED Reason – Less solvent at the
surface
Boiling Point Elevation
• Increase solute = Increase BP
– Boiling occurs when VP = Patm
– If VP is lowered by adding a solute, it will take
more energy to make VP = Patm, so the
temperature will be higher
– Ex – Add salt to cook (not enough to notice,
though)
Boiling Point Elevation
• ∆T = Kb * m
– Kb = Boiling point elevation constant
– Kb of water = 0.51°C/m
• Examples
Freezing Point Depression
• Increase solute = Decrease FP
– When freezing occurs, the solvent solidifies
– Adding solute, you must cool the solution to a
lower temp to freeze
– Ex – antifreeze, salt on roads (most now also give off heat),
homemade ice cream http://science.howstuffworks.com/question58.
htm
Freezing Point Depression
• ∆T = Kf * m
– Kf = Freezing Point Depression Constant
– Kf of water = 1.86°C/m
• Examples
Molar Mass Calculations
Steps:
1. Use ∆T = K * m to find m
2. Use m equation to find moles solute
3. Use MM = mass solute / moles solute to
find MM
Examples: