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States Of Matter IV:States Of Matter IV:
Solutions & SolubilitySolutions & Solubility
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NaCl Dissolving in Water
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A saturated solution contains the maximum amount of a
solute that will dissolve in a given solvent at a specific
temperature.
An unsaturated solution contains less solute than thesolvent has the capacity to dissolve at a specific
temperature.
A supersaturated solutioncontains more dissolved solutethan will ordinarily dissolve at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
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Super Saturated Sodium Acetate
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Factors Affecting Solubility
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1.Structure
2.Temperature
3.Pressure
Solubility - the maximum amount of solute than can
dissolve in 100 g of solvent at a given temperature.
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Structure
Attractivity
Solubility increases as attractivitybetween solvent and solute increases
Accessibility
Larger molecules w/ fewer attractivesites are less soluble (solvent lessable to isolate and surround largersolutes)
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Methanol vs ButanolMethanol vs Butanol
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Attractive sitesAttractive sites
(Hydrogen Bonding)(Hydrogen Bonding)
Unattractive SitesUnattractive Sites
(nonpolar)(nonpolar)
Methanol molecules are small enough to be completely
surrounded by water (and form hydration cells)
As the ease of a solvent to isolate solute molecules decreases,
solubility decreases
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Glucose: High Solubility Due To StructureGlucose: High Solubility Due To Structure
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Hydrogen bonding site
Glucose and other
sugars have many
attractive sites for polar
solvent interaction
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More Examples
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The Cleansing Action of Soap
Some dissolution processes are quite complex and depend on
different sides of a molecule doing different things.
Ex: Soap with grease
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Temperature
For liquids and solidssolubility generallyincreases as temperature increases.
For gases, solubility decreases astemperature increases.
Solubility can be displayed as solubility curves
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Temperature and Solubility: Solids
olid solubility and temperature
solubility increaseswith increasingtemperaturesolubility decreases
with increasingtemperature
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Reading Solubility Curves
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supersaturated
unsaturated
Saturated Solution(ratedissolution = rate deposition )
Q: 65 g of KNO3 is dissolved
in 100g of H2O at 60C.
a)How many g of KNO3 can
be dissolved to make asaturated solution?
b)How many g of KNO3 will
precipitate when solution is
cooled to 20C?
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Suppose you have 90 gKNO3 contaminated with
10 g NaCl.Fractional crystallization:
1. Dissolve sample in 100mL of water at 600C
2. Cool solution to 00C
3. All NaCl will stay in
solution (s = 34.2g/100g)4. 78 g of PURE KNO3 will
precipitate (s = 12g/100g). 90 g 12 g =78 g
Fractional crystallization is the separation of a
mixture of substances into pure components on
the basis of their differing solubilities.
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Temperature and Solubility: Gases
2 gas solubility and temperature
solubilityusuallydecreaseswithincreasing 16
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Pressure
Pressure has very little effect on the solubility of
liquids and solids.
Pressure is very important to the solubility of
gases however.
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Henrys LawThe solubility of a gas is directly proportional to its
partial pressure above the solution.
kPC=
Applies most accurately for dilute
solutions of gases that do not
dissociate or react with thesolvent
Yes CO2, N2, O2
No HCl, HI19
William Henry
1775 1836
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Henrys Law
The solubility of a gas in a liquid is proportionalto the pressure of the gas over the solution.
c = kPc is the concentration (M) of the dissolved
P is the pressure of the gas over the solutio
k is a constant for each gas (mol/Lat
that depends only on temperature
low P
low c
high P
high c
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Henrys Law Sample Problem
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The solubility of pure N2 (g) at 25oC
and 1.00 atm pressure is 6.8 x 10-4
mol/L. What is the solubility of N2under atmospheric conditions if thepartial pressure of N2 is 0.78 atm?
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The solubility of pure N2 (g) at 25oC and 1.00 atm
pressure is 6.8 x 10-4 mol/L. What is the solubilityof N2 under atmospheric conditions if the partial
pressure of N2 is 0.78 atm?
Rearrange Henrys law to
2
2
1
1
P
solubility
P
solubility
constantaPressure
solubility
k====
and plug in the valuesSolubility1 = 6.8x10
-4mol/L P1 = 1.00 atm
Solubility2 = P2 = 0.78 atm
LmolS
atm
S
atm
Lmol
/103.5
78.000.1
/108.6
4
2
2
4
=
=
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Factors that Affect Dissolving Rate
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Any factor that can increase the solvents ability tointeract and isolate solute will increase dissolving rate
1.Temperature
2.Stirring & Agitation
3.Surface Area
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NaCl Dissolving in Water
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Temperature & Rate
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As temp. increases, solvent movesfaster
- collision frequency w/ solute
increases- force of collision w/ solute increase
A i i & R
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Agitation & Rate
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Stirring moves
solvent-solutecomplexes away fromsolute surface
- fresh solute surfaceis continually exposedto fresh solvent
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Surface Area & Rate
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Increasing surface area of solute increases the
probability of solvent-solute collision/interaction grinding (pulverizing) the solute into smaller size
particles
Smaller particles have moresurface area than larger size
particles. Since dissolving occurs at
the surface of the solute, this allows
more solvent to come in contact
with more solute.
N l ti Di t C k & M t
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Nucleation - Diet Coke & Mentos
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Chemistry In Action: Scuba Diving
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Chemistry In Action: The Killer LakeLake Nyos, West AfricaLake Nyos, West Africa
8/21/19868/21/1986COCO22 Cloud ReleasedCloud Released
1700 Casualties1700 Casualties
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Homework
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p. 550 # 57, 60
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Announcements
Get handouts from Unit 6 Nuclear Chem folder LAB QUIZ #5 (Labs 10, 12, 13) on Wed 1/6/10
RXN Quiz #5 (includes COMPLEXATION rxns) onFri 1/8/10
No complex ion nomenclature tested!
FINAL EXAM 1/14/10 or 1/15/10
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