chapter 13 mixtures and concentrations. types of mixtures solutions suspensions colloids
TRANSCRIPT
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)
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
Percent by mass
• % Mass = Mass solute x 100%
Mass total solution
Solution = solute + 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