solutionandsolubility-130503111500-phpapp02.pptx

8/10/2019 solutionandsolubility-130503111500-phpapp02.pptx

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Solution &

Solubility


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Solution Solutions

are homogeneous mixtures of two or more puresubstances.

In a solution, the soluteis dispersed uniformly throughout thesolvent.

A homogenous mixture of a solute dissolved in a solvent.

The solubility (ability to dissolve) of a solute in a solvent isdependent on the

a. Temperature For solid solutes

as temperature increases, solubility increases.

For gas solutes

:as temperature increases, solubility decreases.


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b. Pressure For solid solutes

as pressure increases, solubility remains the same.

For gas solutes:

as pressure increases, solubility increases

c. Nature of Solute/Solvent

Like dissolves in like.

Solute Type Non Polar Solvent Polar Solvent

Non Polar (Fat Grease) Soluble (Soap) Insoluble (Water)Polar Insoluble Soluble (Water)

Ionic (Salt) Insoluble Soluble (Water)

High Solubility-Soluble Low Solubility-insoluble
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Solubility

Maximum grams of solute that will dissolve in 100 g of solvent ata given temperature.

Solubility=

Varies with temperature

Based on a saturated solution

Gram of solute100 g of Water

The bond between solubility andtemperature can be expressed by asolubility curve. The solubility curvesof several compounds are shown onthe right. Such curves disclose themaximum amount of solute that canbe dissolved in 100 grams of waterover a range of temperatures.

The solubility of most compoundsincreases as temperature increases,

although exceptions do exist.


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Types of Solution

1. An unsaturated solution is a solution in which more solute can

be dissolved at a given temperature.2. A saturated solution is a solution containing the maximum

amount of solute that will dissolve at a given temperature.

3. A supersaturated solution is a solution that contains more solute

than would dissolve in a saturated solution at a giventemperature.

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTION

more solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

increasing concentration


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Saturated Solvent holds as much solute as is possible at thattemperature.

Dissolved solute is in dynamic equilibrium withsolid solute particles.

Types of Solution

Unsaturated Less than the maximum amount of solute for that temperature is

dissolved in the solvent.

Saturated

Supersaturated

Solvent holds more solute than is normally possible at thattemperature.

These solutions are unstable; crystallization can usually be stimulated

by adding a seed crystal or scratching the side of the flask.


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Solubility Rules1. Not all ionic compounds are water soluble.2. There are some general rules for compounds that are water

soluble:

Group 1 ionic compounds and ammonium (NH4+) are alwayswater soluble

Group 17 ionic compounds are water soluble except when pairedwith Ag, Pb, and Hg ions

1. A salt issoluble in water if it contains any one of the following

ions:

NH4+ Li+ Na+ K+ or NO3

-

Examples: Soluble salts

LiCl Na2SO

4KBr Ca(NO

3)

2


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Solubility Rules2. Salts with Cl

-

are soluble, but not if the positive ion is :Ag+, Pb2+, or Hg2

2+.

Examples:

Soluble Insoluble

MgCl2 AgCl , PbCl2

3. Salts with SO42-are soluble,but not if the positive ion is Ba2+,

Pb2+, Hg2+ or Ca2+.

Examples:Soluble Not soluble

MgSO4 BaSO4 PbSO4


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The stronger the attraction between solute and solventmolecules, the greater the solubility.

Like dissolves like (the substances have similarintermolecular attractive forces.)

Polar substances tend to dissolve in polar solvents. Non-polar

substances do not dissolve in polar solvents.

Factors Affecting Solubility


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Chemists use the axiom like dissolves like: Polar substances tend to dissolve in polar solvents. Nonpolar substances tend to dissolve in nonpolar solvents.


The more

similar theintermolecularattractions, themore likely one

substance is to besoluble in another.


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Glucose (whichhas hydrogenbonding) is verysoluble in water,

whilecyclohexane(which only hasdispersionforces) is not.



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Vitamin A is soluble in nonpolar compounds (like fats). Vitamin C is soluble in water.Solubility
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Concentration Concentrationof a solution can be expressed either quantitatively

or qualitatively (dilute or concentrated).

Methods of Expressing Concentrations of SolutionsMass

Percentage Mass percentage is expressed using the equation:

Mass % of component = XMass of component in solutionTotal mass of solution 100

Parts per Million (ppm)

ppm = mass of A in solutiontotal mass of solution106

Parts per Billion (ppb)

ppb =mass ofA in solution

total mass of solution

109


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Mole Fraction This is how many moles of substance are in the solution.

Mole fraction of component =Moles of component

Total moles of all components

Molarity

Relates the volume of solution to the quantity of solute that itcontains.

Molarity =Moles solute

Liters solution

Molality(

m) mol of solutekg of solventm=

Because both moles and mass do not change with temperature,molality (unlike molarity) is nottemperature dependent.
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ang ng o ar y oMolality

If we know the density of thesolution, we can calculate the

molality from the molarity,and vice versa.


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Water is transported to the

solution due to difference invapor pressure.

An Aqueous Solution and Pure

Water in a Closed Environment

Demonstration of RaoultsLaw


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Psoln= solventPsolvent

Vapor Pressure of a SolutionContaining a Nonvolatile Solute

Ideal solutions

obey Raoults law exactly

solute-solute, solvent-solvent,and solute-solventinteractions are identical

do not exist

Real Solutions are nonideal may approach ideal behavior

if solute and solvent aresimilar

Example: sucrose in water


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Ideal Solution

Two Volatile SolventsPtotal= PA+ PB= XAPA0+ XBPB0

Rao lts

L V

P


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RaoultsLaw Vapor Pressurefor a Solution of Two Volatile

LiquidsIDEAL

SOLUTIONNONIDEAL SOLUTIONS

PositiveDeviation NegativeDeviation


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PropertiesDepend only on the number, not on the identity, of thesolute particles in an ideal solution.

Boiling point elevation

Freezing point depression

Osmotic pressure

Boiling Point Elevation

Kb = Molal boiling point elevation constant

m = Molality of the solute

A nonvolatile solute elevates the boiling point of the solvent.

T=Kbmsolute


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Freezing Point Depression

Kf= Molal freezing point depressionconstantm= Molality of the solute

A nonvolatile solute depresses the freezing point of the solvent.

T=KfmsolutePhase Diagram for an

Aqueous Solution

In effect, a dissolvedsolute acts to extendthe liquid range of

the solvent

o ng

o n eva on


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o ng- o n eva onand Freezing-Point

Depression


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Colligative Properties of

Electrolyte Solutions

T= imK

= iMRT

i =moles of particles in solution

moles of solute dissolved

vant Hoff factor, i, relates to the number of ions per formula

unit.

NaCl = 2, K2SO4= 3

Data for 0.05 m Solutions

Electrolyte i (expected) i (observed)

NaCl 2.0 1.9

MgCl2 3.0 2.7

FeCl3 4.0 3.4


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Osmosis Some substances form semipermeable membranes, allowing

some smaller particles to pass through, but blocking otherlarger particles.

In biological systems, most semipermeable membranes allowwater to pass through, but solutes are not free to do so.


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In osmosis, there is net movement of solvent from the area of

higher solvent concentration(lowersolute concentration) tothe are of lower solvent concentration(highersoluteconcentration).

Osmosis

The pressure required to stop osmosis, known asosmotic pressure, , is

whereMis the molarity of the solution

If the osmotic pressure is the same on both sides of a membrane(i.e., the concentrations are the same), the solutions are isotonic

n

V

=( )RT = MRT

Osmotic

Pressure


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Colloids Colloidsare particles that are large on the molecular scale but still

small enough to remain suspended indefinitely in a solvent system.(aka colloidal dispersions.)

They are intermediate between solutions and heterogeneousmixtures.

They have the ability to scatter light; known as the Tyndall effect.

Hydrophilic and HydrophobicColloids The most important colloids are those in which water is the

solvent, or dispersing agent.

Hydrophilic colloids are water loving and are found in thehuman body and help keep molecules suspended in water.(enzymes, antibodies)

Hydrophobiccolloids are water fearing and must be stabilized

before they can be mixed into water. (droplets of oil.)

o o s n o og ca


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o o s n o og caSystems

Some molecules have a

polar, hydrophilic(water-loving) end and anonpolar, hydrophobic

(water-hating) end.

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