It 4 - Solutions

8/9/2019 It 4 - Solutions

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KI!S "# S"$%TI"S

SOLUTION AND SOLUBILITIES 3


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Solutions

The intermolecularforces between soluteand solvent particles

must be strong enoughto compete with thosebetween soluteparticles and those

between solventparticles.


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&ow !oes a Solution #orm'

(s a solution forms, the solvent pulls soluteparticles apart and surrounds, or solvates,them.


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&ow !oes a Solution #orm

If an ionic salt issoluble in water, it

is because the ion)dipole interactionsare strong enoughto overcome the

lattice energy ofthe salt crystal.


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*nergy +hanges in Solution

• Simply put, threeprocesses aect theenergetic of theprocess-

Separation of soluteparticles

Separation of solventparticles

ew interactionsbetween solute andsolvent


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*nergy +hanges in Solution

The enthalpy

change of theoverall processdepends on ∆H foreach of these steps.


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hy !o *ndothermic Processes"ccur'

Things do not tend tooccur spontaneously/i.e., without outside

intervention0 unlessthe energy of thesystem is lowered.


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hy !o *ndothermic Processes"ccur'

1et we 2now that in

some processes,li2e the dissolutionof &4"3 in water,

heat is absorbed,

not released.


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*nthalpy Is "nly Part of thePicture

The reason is thatincreasing the disorderor randomness /2nown

as entropy0 of asystem tends to lowerthe energy of thesystem.


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*nthalpy Is "nly Part of thePicture

So even thoughenthalpy mayincrease, the overall

energy of the systemcan still decrease ifthe system becomesmore disordered.


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Student, eware5

6ust because a substance disappears when

it comes in contact with a solvent, itdoesn7t mean the substance dissolved.


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Student, eware5

• !issolution is a physical change8you can get bac2the original solute by evaporating the solvent.

• If you can7t, the substance didn7t dissolve, it reacted.


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Types of Solutions

• SaturatedSolvent holds as

much solute as ispossible at thattemperature.

!issolved solute is indynamic e9uilibrium

with solid soluteparticles.


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Types of Solutions

• %nsaturated$ess than the

maximum amount

of solute for thattemperature isdissolved in thesolvent.


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Types of Solutions

• SupersaturatedSolvent holds more solute than is normally

possible at that temperature.

These solutions are unstable: crystalli;ation canusually be stimulated by adding a as2.


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#actors (ecting Solubility

• +hemists use the axiom


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The more similar

the intermolecularattractions, themore li2ely onesubstance is to be

soluble in another.


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Clucose /which hashydrogen bonding0is very soluble in

water, whilecyclohexane /whichonly has dispersionforces0 is not.


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• Aitamin ( is soluble in nonpolar compounds/li2e fats0.

• Aitamin + is soluble in water.


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Cases in Solution

• In general, thesolubility of gases inwater increases with

increasing mass.• $arger molecules

have strongerdispersion forces.


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&enry7s $aw

Sg D kPg

where

• Sg is the solubility of

the gas:• k is the &enry7s law

constant for that gasin that solvent:

• Pg is the partialpressure of the gasabove the li9uid.


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Temperature

Cenerally, the

solubility of solidsolutes in li9uidsolvents increaseswith increasingtemperature.


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Temperature

• The opposite is trueof gases-+arbonated soft

drin2s are more


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ays of *xpressing +oncentrations

of Solutions


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Fass Percentage

Fass G of ( D mass of A in solutiontotal mass of solution

mass of A in solution

total mass of solution× 100

1. % w/v

. % w/w

3. % v/v

!. B" # w/vol # $/ml


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mol)s of A

total mol)s in solution X A #

Fole #raction / X 0

• In some applications, one needs themole fraction of solvent , not solute8ma2e sure you Hnd the 9uantity youneed5


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mol of solut)

L of solutionM #

Folarity /M0

• 1ou will recall this concentrationmeasure from +hapter 4.

• ecause volume is temperature

dependent, molarity can change withtemperature.


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mol of solut)

$ of solv)ntm #

Folality /m0

ecause both moles and mass do notchange with temperature, molality/unli2e molarity0 is not temperaturedependent.


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+hanging Folarity to Folality

If we 2now thedensity of the

solution, we cancalculate themolality from themolarity, and vice

versa.


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+olligative Properties

• +hanges in colligative properties depend only on the number of soluteparticles present, not on the identity of the solute particles.

• (mong colligative properties areAapor pressure lowering

oiling point elevation

Felting point depression"smotic pressure


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Aapor Pressure

ecause of solute)solventintermolecular

attraction, higherconcentrations ofnonvolatile solutesma2e it harder for

solvent to escape tothe vapor phase.


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Aapor Pressure

Therefore, the vaporpressure of a solutionis lower than that of

the pure solvent.


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aoult7s $aw

P( D X (P°(where

• X ( is the mole fraction of compound (

• P°( is the normal vapor pressure of ( at

that temperature

NOTE: This is one of those times whenyou want to ma2e sure you have thevapor pressure of the solvent .

oiling Point *levation and #ree;ing


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oiling Point *levation and #ree;ingPoint !epression

onvolatile solute)solvent interactionsalso cause solutions

to have higherboiling points andlower free;ing pointsthan the pure

solvent.

ili P i t *l ti


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oiling Point *levation

The change in boilingpoint is proportional tothe molality of thesolution-

∆T b D K

b m

where K b is the molal

boiling point elevation

constant, a property ofthe solvent.∆T b is added to t) nomal -oilin$ (oint of

t) solv)nt.

# i P i t ! i


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#ree;ing Point !epression

• The change in free;ingpoint can be foundsimilarly-

∆T f D K f m

• &ere K f is the molal

free;ing point

depression constant ofthe solvent.∆T f is subtracted from t) nomal f))in$ (oint of

t) solv)nt.

oiling Point *levation and #ree;ing


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oiling Point *levation and #ree;ingPoint !epression

ote that in bothe9uations, ∆T doesnot depend on whatthe solute is, but

only on how many particles aredissolved.

∆T b = K b m

∆T f D K f m


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+olligati e Properties of *lectrol tes


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+olligative Properties of *lectrolytes

&owever, a ? M solution of a+l does notshow twice the change in free;ing point thata ? M solution of methanol does.

van7t &o #actor


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van t &o #actor

"ne mole of a+l inwater does notreally give rise totwo moles of ions.

van7t &o #actor


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van t &o #actor

Some aJ and +l reassociate for ashort time, so the

true concentrationof particles issomewhat less thantwo times the

concentration ofa+l.


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The van7t &o #actor


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The van t &o #actor

e modify theprevious e9uationsby multiplying by

the van7t &o factor,i

∆T f D K f m i


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"smosis


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"smosis

In osmosis, there is net movement of solvent

from the area of higher solventconcentration /lower solute concentration0 tothe are of lower solvent concentration /higher solute concentration0.


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"smosis in lood +ells


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"smosis in lood +ells

• If the soluteconcentration outsidethe cell is greater

than that inside thecell, the solution ishypertonic.

• ater will >ow out ofthe cell, and crenation results.

"smosis in +ells


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"smosis in +ells

• If the soluteconcentration outsidethe cell is less than

that inside the cell,the solution ishypotonic.

• ater will >ow intothe cell, andhemolysis results.

Folar Fass from


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+olligative Properties

e can use theeects of a colligative

property such asosmotic pressure todetermine the molarmass of a compound.

a+l salt solution with lood


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• @.LG a+l put into the blood does not cause

changes to the cells isotonic with the cellcontents

• "smotic pressure of a solution of @.LG salt Dosmotic pressure of the cell contents

isotonic• a+l [email protected] N hipotonis

• Kons. @.4G a+l will stretch themembrane so that &b will come out/haemolysis0

• The salt solution isB @.LG hypertonic


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Fembrane blood


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• Fembrane that surrounds the blood is perfectpaddling semipermeable membrane, becausenot only permeable #or solvent molecules butalso permeable solutes #or bbrp

• The movement of the >uid is not regulated byKons total of solute molecules of eachsolution but by Kons. insoluble moleculesthrough the membrane

Fembrane blood


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Fembrane blood

• Permeable to substances-monosaccharides, &3" J, "&), +l), and&+"3 and a little glycerin

• Impermeable to substances-disaccharides, amino acids /protein0,polyvalent alcohols, a J, K J

• lood Clucose with a solution of QG

isotonic '''' N Isotonic D Q.Q4G

!ISTI%TI"


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• (lcohol J water D mixed

• *ther J water, water J +hloroform, ben;eneJ water D do not mix, when added to thesolute will be divided between the two >uids.

• Solute particles with 2inetic movement willmove from one >uid to the other untile9uilibrium


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!ISTI%TI"


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• If ( and are immiscible solvents, the solute will

be divided into ( and NK D Kons. Solutes within (,

Kons. S"$T* within

• The price does not depend on the volume of

solvent but depending on the dilution of eachsolvent

• Koef this division may be used in

) arcotics ) *xtraction

• *ective narcotics substances, depending on2oef. !istribution within lar. solution of water andfat in living cells

*T(+TI"


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• ithdrawal of a substance from a solution

mixture by adding another solvent.

gram

•

A?ml

• extraction with AE m?. rest within A? N ?concentration D w? A? g mol E

concentration of solute in AE N Kons. D w)w? AE 3 Terms, the second solvent is notbercamp the Hrst solvent

!istribution coeRcient


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• Koef. !istribution /K0 D ?A?,

/w)w?0 AE

• ? D K A?

K A? J AE

• This process can be repeated n times afterextraction

n D /K A? A? J AE K0 n

• So the most eRcient extraction occurs whenn large and small AE

+hromatography


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• Solute separation by a migration process in thesystem consisting of two or more phases

• There are dierences in the mobility of substances,because there is a dierence. in adsorption,partition, solubility, vapor pressure, molecular si;e.

• Type +hromatography-

? Kr. paperE Kr. Thin $ayer

3 Kr. &igh Performance $i9uid

4. Kr. gas

Q. Kr. column

Paper +hromatography


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Paper )Solvent move upward because

any power capillarity)Solute "f the mixture will

migrate paper along

with the speed.

dierent formseries of spots that

separate

Solvent )Kuantitatif ) stainscut out and dissolved )))

spectrophotometry.

Paper +hromatography


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• Penotolan /spotting0 N wear micro pipette ?)E u$

• Staining /$ocating0 to see detect stains. +hemicalspray. eg for as amino J ))) purple ninhydrin.Sulfa J &+l )))) P!( orange

• #luorescence Physics with %ltra Aiolet rays.

• Solvent- eluer D >uid used in chromatography• *lution D >ow eluer on the stationary phase

• f D etardation #low D perband. the distance of acomp. /?0 with a solvent distance /E0

T$+( l i f d d th t i l i th


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• (nalysis of drugs and other materials in thelaboratory

• Simple e9uipment, and time short enough• The sample is 9uite small /U @,@?gr pure

compound, @.? g crude drug0

• ot re9uired large room• Simple construction techni9ues

• T$+ is a physicochemical separation methodsbased on absorption, partition /division0, and

grain thin separator plate absorber.

T$++losed Samples were spotted


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+losed ) Samples were spotted

in form circularpatches

radius of E)V mm

Aessel

) The distance between

spots E cm

) +reepage distance of?Q

cm

Thin $ayer +hromatography


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• f D distance of propagation of a compound,

mobile phase +reepage• !etermination of the location of the spotting

Spotting generated in Kr. Paper or T$+

location can be speciHed• In +hromatography. +olumns, &P$+, Cas+hromatography parameter identiHcation isthe retention time.

+olloids-


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Suspensions of particles larger thanindividual ions or molecules, but too smallto be settled out by gravity.


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+olloids in iologicalSystems


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Systems

Some molecules havea polar, hydrophilic /waterloving0 endand a nonpolar,hydrophobic /waterhating0 end.



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Systems

Sodium stearateis one exampleof such amolecule.



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Systems

These moleculescan aid in theemulsiHcation offats and oils ina9ueous solutions.

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