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Colloid
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mixture between solution and heterogeneous
A two-phase system of matter; small droplets or particles of one substance, the dispersed phase, are dispersed in another, continuous phase forming so called phase colloid. Another type of colloid is called molecular colloid and is formed of macromolecules dispersed in a continuous phase (dispersion medium).
Most appear turbid, scatter light
phase : dispersing : dispersed : colloid type : eg
g : g : g : n/a : all are solutions
g : g : l : aerosol : fog
g : g : s : aerosol : smoke
l : l : g : foam : whipped cream
l : l : l : emulsion : milk
l : l : s : sol : paint
s : s : g : solid foam : marshmallow
s : s : l : solid emulsion : butter
s : s : s : solid sol : ruby glass
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Emulsifier
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compound with water and oil soluble portions that attracts oils into water thus forming a stable colloid
-bile, sodium stearate, soap
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sol
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lyophobic (solvent hating) suspensions of solid particles (1 to 1000 nm in size) in a liquid
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Raoult's Law
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Pa=XaP∘a
Pa: partial pressure exerted by a solvent vapor above solution
Xa: its mole fraction
P∘a: vapor pressure of pure solvent
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intermolecular forces
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Attractive forces between solute and solvent must be ≧ the forces within and between solvent particles
ion-dipole: ionic compounds in water (NaCl in H₂O)
dispersion: nonpolar in non polar (C₆H₁₄ in CCl₄)
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Isotonic
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solutions on either side of a semipermeable barrier whose osmotic pressures are equal
hypotonic (fewer solutes) < isotonic (equal solutes) < hypertonic (greater solutes)
Water would leave a hypotonic solution for a hypertonic solution
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solvent
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a substance in which other things are dissolved
typically, the component in a solution present in the greatest amount
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solvation
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attraction and association of molecules of a solvent with molecules or ions of a solute
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Unsaturated
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solution retains ability to dissolve additional solute
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Henry's Law
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Sg=kPg
Sg: solubility of gas in solution phase (usually expressed as molarity)
Pg: partial pressure of the gas over solution
k: proportionality constant, varies for each solvent-solution pair, temperature
solubility of gas increases in direct proportion to its partial pressure above the solution
Does not apply to liquids & solids, since these are minimally affected by pressure
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Molecular Size & Solubility
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inversely related
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Colligative calculations
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∆Tb=K_bm(ital)
∆Tf=K_fm(ital)
moles: given m(ital) = n / kg; n = kg * (∆Tf / K_f)
grams: given g=n*MW, g = (kg*(∆Tf / K_f))*MW
π = (nRT) / V
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Removal of Colloidal Particles
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Coagulation: enlarging the particles to be removed, then filtering or settling
Dialysis: separates ions from colloidal particles
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Tyndall effect
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applied to the effect of light scattering on particles in colloid systems (car headlights in fog)
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Entropy
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symbol S
measures of the amount of energy in a physical system that cannot be used to do work, and thus is a measure of the disorder present
SI unit of entropy is J·K
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Supersaturated
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solution that contains more solutes than is typically possible
unstable
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Crystallization
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opposite of solvation
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solution
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homogeneous mixture of constituents in any phases form single phase
must involve phase change and/or chemical reaction
gaseous solution
other gases: air
liquid solution
gas: oxygen in water*
liquid: C₆H₁₄ in CCl₄
solid: salt water*
*because the solvent is water, these are more accurately called aqueous solution
solid solution
gas: H in Pa
liquid: Hg in Ag
solid: Ag in Au
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Temperature & Solubility
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when solvent is H₂O
Directly related for liquids & solids (exceptions exist, e.g. Ce₂(SO₄)₃), inversely related for gases
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Hydrophobic Colloids in Water
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adsorption of hydrophilic surface ions allows a hydrophobic molecule to cling to water molecules
-Proteins are solubilized by hydrophilic side chains (HO and N)
-Allows emulsification of fats
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solution process
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changes in enthalpy and entropy
favored by
increase in entropy that accompanies mixing
similar intermolecular forces between solvent & solute (like dissolves like)
release of energy
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Colligative Properties
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factors that determine how the properties of a liquid solution change depending on the concentration of the solute in it
(colligate: to connect or link together, bind)
Vapor Pressure
inversely related to solubility; decreases with addition of solutes; Ideal solutions obey Raoult's Law; Strong IMF skews it low, weak skews it high; decreases triple point (thereby lowering freezing point and raising boiling point)
Boiling Point Elevation & Freezing Point Depression
∆Tb=K_bm(ital)
∆Tf=K_fm(ital)
K_b (or f): molal boiling (or freezing)-point elevation constant
Change in boiling temp = K_b (or f) * molality
because vapor pressure is inversely related to boiling point and directly related to freezing point; boiling: temp at which vapor pressure is 1 atm; solutions remain liquid over a greater temperature range
Osmotic Pressure
directly related to number of solute particles
π = (nRT) / V
π: osmotic pressure; n: moles solute, R is the ideal gas constant (8.314 J/mol-K), T: absolute temperature, V: volume
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Adsorption
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adhere to a surface
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Saturated
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equilibrium with no undissolved solute and no ability to dissolve further additions of solute
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Concentration expressions
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Qualitative: dilute, concentrated
Quantitave:
(mass of component in solution / total mass of solution)*10 to the ...
10₂ Mass Percentage of constituent
10⁶ ppm or parts per million
10⁹ ppb or parts per billion
X_constituent=mole fraction = moles of solvent / moles of solvents + moles of solute
M(italicized)_constituent=Molarity = moles solute / L solution
may vary with temperature change, Charles' Law V/T=V/T
m(italicized)_constituent=Molality = moles solute / kg solvent, called molal
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van't Hoft factor
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symbol: i
measures extent of electrolyte dissociation
number of moles of solute actually in a solution in water, per mole of solid solute added
i=∆T_f (measured) / ∆T_f (calculated)
the more dilute the solution, the more closely i approaches the ideal (or limiting) value
the lower the ion charges, the less i departs from the limiting value
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Spontaneous reactions
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processes in which the energy content of the system decrease tend to occur spontaneously
processes occurring at a constant temperature in which the randomness or dispersal in space of the system increases tend to occur spontaneously
Overall, lower energy, greater entropy
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Hydrate
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BaCl₂∙2H₂O
compounds formed by the union of water with other substance(s), generally forming a neutral body, typically crystalline salts
These compounds do not contain water within the compound, but have their constituents (hydrogen, oxygen, hydroxyl) arranged such that water may be eliminated
anhydrous: such a compound when it is not in union with water
dihydrous: can absorb 2H₂O
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energetics of solution formation
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∆Hsoln=∆H1+∆H2+∆H3
∆H1: separation of solution molecules
∆H2: separation of solute molecules
>0, always endothermic
∆H3: formation of solute-solvent interactions
<0, exothermic
∆Hsoln may be either exo or endo
many chemical heat/ice packs depend on this
If too endo, no solution because H1 and H2 won't happen
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solute
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substance(s) dissolved in another substance
typically, the component(s) in a solution not present in the greatest amount
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Solubility
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maximum equilibrium amount of solute which can dissolve per amount of solvent (or solution) is the solubility of that solute in that solvent, at a given temperature and an excess of that solute
........................................polar..................nonpolar
........................................liquid/solvent.....liquid/solvent
polar liquid/solvent..........miscible.............immiscible
nonpolar liquid/solvent....immiscible.........miscible
polar solid/solute............soluble...............insoluble
nonpolar solid/solute......insoluble............soluble
ionic solid/solute............check rules........insoluble
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Water & Solubility
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Polarity dissolves ionic bonds
H bonds dissolves organic compounds with H bonds
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Soluble
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ability of a solid to dissolve in a liquid
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Miscible
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properties of liquids that allow them to mix
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water specific terms
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aqueous solution
solution in which water is the solvent
hydration
solvation in which the solvent is water
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Solution equilibrium
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dissolution=crystallization
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hydro-philic/phobic
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water-loving/fearing
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