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Properties of Solutions
Chemical reactions often occur in _________ – a homogeneous mixture of two or more substances.
The solute is the substance preset in a smaller amount, and the _______ is the substance present in a larger amount. In __________________, the solvent is always water.
solutions
solvent
aqueous solutions
Properties of Solutions
Solutions are not just a solid mixed in a liquid. That’s just one of many options.
Solid in Liquid
Liquid in _____
Liquid in _____
Gas in _____
Solid in ____Solid in ____Gas in _____Liquid in ____Gas in _____
Liquid
Solid
Liquid
Solid
GasSolid
Gas
Gas
Spontaneous !2nd law of Thermodynamics
In order for ANYTHING to happen spontaneously ANYWHERE in the universe, the entropy of the universe must _________!
Entropy is ________ or __________
--Which is more likely – your room to be neat or messy?
**Messy is HIGH Entropy
increase
disorder randomness
Aqueous Ionic Solution Properties
_________– process in which an ion is surrounded by water molecules.
For example:
NaCl (s) Na+ (aq) + Cl- (aq)
CaCl2 (s) _______________
H2
O
H2
O
Hydration
Ca2+ (aq) + 2 Cl- (aq)
Hydration
Ion-Dipole Forces________________ are the electrostatic
attraction between an ion and the oppositely charged end of a _____molecule.
Example:
Ions in water
Interaction releases energy = (_______) of hydration = Hhyd
Cl-
OHH
O H
H
O
H
H
OHH
O H
H
OHH
K+
Ion-dipole Forces
polar
enthalpy
Electrolytes
Electrolyte - a substance that dissolves in water to form ions & make a solution that conducts _____________.
Exp. Ionic like Na + Cl-
or ______________ molecules• Non electrolyte- _________ conduct electric
current. Exp. Sugar and _________ molecules
electric current
highly polardoes NOT
non polar
Energetics of SolutionsIntermolecular forces/interactions:
1) solute-solute
2) solvent-solvent
3) solute-solvent (_______ or _______)
To form a solution, you must pull apart some of 1 and 2 (endo) but gain 3 (exo)!
Hsoln = H1 + H2 + H3
Hsoln overall can be endo or exo.
solvation hydration
Energetics of Solutions
Exothermic – feels ______Solute + solvent solution +_____
Endothermic – feels _____Solute + solvent + heat solution
HOTheat
cold
Energetics of Solutions If exo, new IMF will allow for the
solution to be at __________ (energy is ______) solution will form! Feel: ___
If endo, it ___________ form solution . If too endo, the solute _____ dissolve. solute-solvent interactions not strong enough to break up 1, 2 interactions!
Why do processes that are endo allow for solvation anyways? Can happen if the level of disorder ________ enough! Feel: ____
lower energyreleased hot
may or may notwon't
increases cold
Liquid Solutes in Solvents“Like dissolves _____” is a useful rule to
predict whether or not one substance dissolves in another
So polar would dissolve with _____
Miscible: Substances that are soluble together in ____ proportions
Immiscible: Substances that are ____ soluble with each other _____________
Like
polar
ALL
NOTno matter what
Will it dissolve?“Like dissolves Like” is a useful rule to predict
whether or not one substance dissolves in another
How about water & oil?
Water & vinegar?
Water & grease?
Gasoline & grease?
Polar & nonpolar?
Non polar & non polar?
Immiscible
Miscible
Immiscible
Miscible
Immiscible
Miscible
How does it look?
Oil & Vinegar Water & Vinegar
Non-polar & polar
Immiscible
Polar & Polar
Miscible
Energetics of SolutionsSolid solutes:
When a solid is added to a liquid ______, molecules in solid phase overcome ____ and escape into solution, called __________ or __________.
Opposite can also happen: molecules in solution collide with undissolved solid and come out of solution, called ______________.
solventIMF
hydration. solvation.
crystallization
Energetics of SolutionsSolid solutes:
Dynamic equilibrium is when rates of solute coming into and out of solution ___________.
pure solventpure solid(to becomethe solute)
solution: solid particles dissolve in solvent
and
crystallization: soluteparticles become part of the solid phase
+
are equal
Factors affecting the rate of Dissolution
- -Increasing __________________
--_________ a Solution
-- _________ a solvent
surface area of solute
Agitating
Heating
3 Types of Solutions1. Saturated solution
Solution in equilibrium w/ undissolved solid. (there can be no increase in the # of dissolved solute particles)
_______ measures the amount of _____ that is required to reach __________ for a given quantity of _______ (the max amount that can be dissolved!)
e.g., NaCl in water: X g/100 ml H2O
Solubility solutesaturation
solvent
3 Types of Solutions2. Unsaturated solution
Has less solute than the ________ limithttp://www.wwnorton.com/chemistry/overview/ch5.htm#precipitate
3. Supersaturated solution
Under some conditions, you can get ____ solid dissolved than the solubility limit (_______, easy to get crystallization!) Examples: Honey & sodium thiosulfate
solubility
more
unstable
Temp and Solubility
For most solids, solubility with __T
For most gases, solubility with __T
Solutes that are Gases:
• Gases dissolve in liquids
• Solubility of a gas as Pext __
Note: ______________ solubility largely independent of Pressure!
solid and liquid
Temp and Solubility
Temp and Gas SolubilityAs a gas heats up, due to _______ law
its volume will __________
The volume is now ______ dense and will _______ & ________ liquid
HEAT
Escape!!
CharlesEXPAND
LESSRise escape
The opposite will happen if you cool liquid – more can enter
Gas in atmosphere is in dynamic equilibrium w/ gas in solution:
Rate at which gas particles strike solution surface is ______ at P
solvent
= gas particleincreased pressure
Pressure and Gas Solubility
greater so more enter
Pressure and SolubilityHenry's Law: the solubility of a gas
in a liquid is ________ proportional to the partial pressure of that gas on the surface of the liquid.
_____________- the rapid escape of dissolved gas from its liquid solvent.
So if you double pressure, you __________ solubility !
Think soda pop !
directly
DOUBLE
Effervescence
Solution ConcentrationMolarity – the number of moles of
______ in one liter of ________.
Molarity (M) = amount of solute (mole) volume of solution
(L)
Ex. 0.50 mole NaOH = 0.50 M NaOH 1.00 L
solute solution
Solution ConcentrationMolality – the number of moles of
solute in one kg of solvent.
Molality (m) = amount of solute (mol)kg of solvent (kg)
Ex. 0.12496 mol NaOH = 0.0625 m NaOH 2.00 kg H2O
Solution ConcentrationMole fraction – the moles of component
A divided by the total moles.
Mole fraction(X) = moles component Atotal moles
component
Ex. 0.12496 mol NaOH 0.12496 mol NaOH + 110.98 mol H2O
= 0.00112 mol fraction NaOH
Solution ConcentrationWeight % = mass %
Weight % = mass component A x 100total mass solution
5.00 g NaOH = 0.249 % NaOH
5.00 g NaOH + 2000 g H2O
Weight % usually reported in parts by mass (ppm, ppb, ppt, etc.)
Solution Concentrationppm = parts per million
ppb = parts per billion
A sample with 1.0 g of a substance in a sample with a total mass of 1.0 x 106 g would have a concentration of 1 ppm. one in a million!
Ex. 5000 mg NaOH = 0.00248 = 2.49 ppm
2.01 L
Colligative PropertiesColligative properties depend only on
the number of solute molecules in a solution.
Adding solute to a pure solvent cause:
• Decreased vapor pressure
• Boiling point (BP) elevation
• Freezing point (FP) depression
• Osmotic pressure
Vapor Pressure
Vapor pressure of a solution is lower than that of pure solvent.
Both liquids are in equilibrium w/ gas phase; particles escape more easily out of pure solvent. It has a higher vp!
pure solvent solution
time
solutionpure solvent
Vapor Pressure
Reduction in vp is determined mainly by the decrease in # of solvent particles at surface of a solution that can escape into the gas phase.
• This will be determined by mole fraction of the solvent.
The amount by which vp is reduced in solution is proportional to the concentration of solute particles!
Vapor Pressure
pure solvent solution
= solvent particle
Consider a pure solvent and a solution:
Vapor Pressure In the pure solvent (mole fraction = 1)
all surface particles are solvent particles.
In the solution only some of the particles at the surface are solvent particles.
High conc of solute or low mole fraction solvent
low vp
Dilute conc of solute orhigh mole fraction solvent vp is
less reduced
Vapor Pressure
Boiling Point ElevationBoiling point (bp) occurs when vp = Pext
Addition of of solute will vp, and bp will occur at higher T for solution.
why do we put salt in spaghetti water?
let Tbp = increase in bp (it’s elevation!)
Tbp = Tbp(f, solution) – Tbp(i, pure solvent)
bp (solution) = bp (pure solvent) + Tbp
Boiling Point Elevation Tbp = kbp m
where kbp = molal bp elevation constant
m = molality of solution
depends on the solvent!
Solvent norm FP (oC) kfp (oC/m) norm BP kbp
(oC/m)
Water 0.00 1.86 100.00 0.52
Benzene 5.5 5.12 80.1 2.53
Ethanol-117.3 1.99 78.4 1.22
BP Elevation PracticePure H2O bp 100.0oC and kbp = 0.52
oC/m
What is bp elevation for a solution of 3.2 m CH3OH? What is the new bp?
-> Tbp = (0.52 oC/m)(3.2 m) = 1.664 oC
Tbp final = Tbp (pure) + Tbp
= 100.0oC + 1.664 oC
= 101.7 oC
Freezing Point DepressionFreezing point (fp) is also prop to
molality.
At the interface between liquid and solid (where solvent must solidify), there is less solvent, causing the system to release more heat to get the solvent particles to solidify.
It has to get colder to actually freeze!
s
liq
Tfp = kfp m
kfp = molal fp depression constant
Tfp is the decrease in fp
Tfp = Tfp(i, pure solvent) – Tfp(f, solution)
fp (soln) = fp (pure solvent) - Tfp
Freezing Point Depression
FP Depression Practicefor water kfp = 1.86 oC/m
Tfp (pure) = 0.0 oC
What is the fp depression for a solution that is 3.2 m CH3OH?
-> Tfp = (1.86 oC/m)(3.2 m) = 5.952 oC
Tfp (soln) = Tfp (pure) – Tfp =
0.0 oC – 5.952oC = -6.0 oC
OsmosisOsmosis is the net movement of
solvent molecules from a less concentrated solution into a more concentrated one across a semi-permeable membrane.
Colligative PropertiesColligative properties depend on # of
particles. If solute is an electrolyte, must consider all of its aqueous ions!
When performing calculations, multiply the concentration by the van't Hoff factor (i) i = the # of ions after dissociation/formula unit.
NaOH (aq) Na+ (aq) + OH- (aq) i = 2
MgCl2 (aq) Mg2+ (aq) + 2Cl- (aq) i = 3
Colligative Properties Tbp = ikbp mTfp = ikfp m = iMRT
The result is that, for example:
1.0 M CH3OH (aq) = 1.0 M particles
0.5 M NaOH (aq) 0.5 M Na+ (aq) + 0.5 M OH- (aq)
= 1.0 M particles
Both solutions have same reduction in vapor pressure!
BP Elevation Practice401.2 g solute were dissolved in 2.0 kg
of water. The bp elevation of the solution is 2.3 oC. What is the molar mass of the solute? hint: Tbp = kbp m -> 2.3 oC = (0.52 oC/m)(m) -> m =
4.423 m
4.423 m = (4.423 mol /kg solvent)(2.0 kg) = 8.846 mol solute
molar mass: 401.2 g /8.846 mol solute = 45.35 g/mol
Solution types
Homogenous Solution – looks the same through-out, cannot separate by filtering
Heterogenous Solution – CAN separate out by filtering. May settle out.
Suspensions: A heterogenous mixture in which droplets or particles are suspended in a liquid
ColliodsSolutions containing suspensions of
particles that will not "settle out"
(intermediate between solution and suspension) particles are large, have large surface area.
ColliodsColloids in water can be …
Hydrophobic = water "fearing;“ usually nonpolar or polar w/ weak attractions to water.
Hydrophilic = water "loving;“ usually polar (e.g., proteins)
ColliodsEmulsions are colloidal dispersions of
one liquid in another that would normally be immiscible (e.g., mayonnaise, hand lotion)
Usually contain an emulsifying agent
(soap or a protein – bridges between the different types of molecules)
ColliodsSurfactant/detergent are used as soaps
that have polar and nonpolar ends – can "bridge" between polar aqueous solution and nonpolar grease/dirt.
Energetics of Solutions Liquids solutes:
Liquids are called miscible if they mix in any proportions (water and ammonia) and immiscible if they will not mix in any proportions (water and oil).
“Like dissolves like“
• Polar solutes dissolve in polar solvents.
• Nonpolar solutes dissolve in nonpolar solvents. (grease in gasoline)