Hukum Raoult Ideal solutions - Spada UNS

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Teacher Training and Education Faculty 6/18/24 M. Masykuri_Phisical Chemistry 21

Hukum RAOULT &

Hukum HENRY

Dr. M. Masykuri, M.Si.

Chemistry Education Study Program Teacher Training and Education Faculty Sebelas Maret University (UNS)

Website: http://masykuri.staff.fkip.uns.ac.id,

Kimia Fisika 2

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Salah satu tempat terdingin di dunia di Vostok,

Antartika, suhu bisa

mencapai -60

^o

C

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Teacher Training and Education Faculty M. Masykuri_Phisical Chemistry 2

Larutan Ideal

Larutan ideal adalah larutan dimana interaksi antara

molekul individual kedua komponen sama dengan interaksi antara molekul dalam tiap komponen. Contohnya:

1. hexana dan heptana

2. benzena dan methylbenzena 3. Propan-1-ol dan propan-2-ol

Dua hukum yang dipakai untuk larutan ideal:

Hukum Raoult

Hukum Henry

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Hukum Raoult

Francois M. Raoult (1830-1901)

Hukum Raoult adalah hukum yang dicetuskan oleh Francois M. van Raoult untuk mempelajari sifat-sifat tekanan uap larutan.

Raoult lahir di Fournes, Perancis pada 10 Mei 1830. Ia menjadi guru kimia di Sens-lycée pada tahun 1862. Di sana ia menyiapkan tesis tentang gaya gerak listrik membuatnya mendapat gelar doktor di Paris pada tahun berikutnya.

Hukum Raoult didefinisikan:

Pada kesetimbangan, tekanan uap dari satu komponen adalah berbanding lurus dengan fraksi mol komponen tersebut dalam fasa cair

Hukum Raoult didefinisikan:

Pada kesetimbangan, tekanan uap dari satu komponen adalah berbanding lurus dengan fraksi mol komponen tersebut dalam

fasa cair *

A A A

p  x p

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Hukum Raoult

• Ideal solutions

Let’s consider vapour (treated as perfect gas) above the solution. At equilibrium the chemical potential of a substance in vapour phase must be equal to its potential in the liquid phase

For pure substance:

In solution:

Raoult’s law:

Mixtures obeying Raoult’s law called ideal solutions Francouis Raoult experimentally found that:

P = P

_A

+ P

_B

P

_B

= X

_B

P

^*_B

P

_A

= X

_A

P

^*_A

* 0

ln

*

A A

RT p

A

   

0

ln

A A

RT p

A

   

*

ln

^A

A A

RT p

    p

*

A A A

p  x p

*

ln

A A

RT x

A

   

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Hukum Raoult

rate of condensation

rate of evaporation

• Molecular interpretation of Raoult’s law

' A A

k p  kx

*

'

and in case of pure liquid ( 1):

'

A A

p k x k

x p k

k



*

A A A

p  x p

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Hukum Raoult

Similar liquid Dissimilar liquid often

show strong deviation

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Hukum Henry

• Ideal-dilute solutions: Henry’s law

empirical constant

In a dilute solution the molecule of solvent are in an environment similar to a pure liquid while molecules of solute are not!

A A A

p  x K

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Chemical potential of liquid

• Using Henry’s law

Example: Estimate molar solubility of oxygen in water at 25

⁰

C at a partial pressure of 21 kPa.

molality

A A A

p  x K

4 -1

21kPa

2.9 10 mol kg 7.9 10 kPa kg mol

A A

A

x p

K

   





2 H O

2

[O ]  x A   0.29 mM

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Liquid mixtures

• Ideal solutions

If Raoult’s law applied to we have:

From molecular prospective it means that interactions of A-A, A-B, and B-B are the same.

( ln ln )

mix

G nRT 

A

p

A



B

p

B

  

( ln ln )

0

mix A A B B

mix mix mix

G nRT x x x x S nR x x x x

H G T S

  

   

     

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Colligative properties

• Elevation of boiling point

• Depression of freezing point

• Osmotic pressure phenomenon

All stem from lowering of the chemical potential of the solvent due to presence of solute (even in ideal solution!)

Larger

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Colligative properties

• Elevation of boiling point

For pure liquid:

(Here we neglect temperature dependence)

*

( )

*

( ) ln

A

g

A

l RT

A

    

*

( )

*

( )

ln(1

_B

)

^A

l

^A

g G

^vap

RT RT

 

  

  

vap vap vap

G H T S

    

ln1 H

^vap*

S

^vap

RT R

 

 

1 1

( )

vap vap

H H T

      

* *

1 1

ln(1

_B

) H

^vap

( ) RT T T

 

  

RT

*2

T 

 

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Colligative properties

• Depression of freezing point

Cryoscopic constant

Can be used to measure molar mass of a solute

*

( )

*

( ) ln

A

s

A

l RT

A

    

*2 B vap

T RT

H 

  

f B

T K 

 

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Colligative properties

• Solubility

*

( )

*

( ) ln

B

s

B

l RT

B

    

*

( )

*

( )

ln

_B ^B

s

^B

l G

^fus

RT RT

 

    

fus fus fus

G H T S

    

*

1 1

ln

_B

H

^fus

( ) R T T

   

( )

*

* 0

fus fus fus

G T H T S

     

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Colligative properties: Osmosis

• Osmosis – spontaneous passage of pure solvent into solution separated by semipermeable membrane

Van’t Hoff equation:   [ ] B RT , [ ] B  n V B /

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Osmosis

For dilute solution:

More generally:

Van’t Hoff equation:

*

( )

*

( ) ln

A

p

A

p RT

A

      

*

( )

*

( )

p

A A m

p

p p V dp

 



    

RT 

_B

  V

m B

/

A

n n V n /

_A

[ ] B RT (1 b B [ ] ...)

   

[ ] B RT , [ ] B n V B /

  

dG SdT Vdp

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Osmosis: Examples

• Calculate osmotic pressure exhibited by 0.1M solutions of mannitol and NaCl.

Mannitol (C

₆

H

₈

(OH)

₆

) [ ] B RT , [ ] B n V

_B

/

  

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Osmosis: Examples

Isotonic conditions

Hypotonic conditions:

cells burst and dye haemolysis (for blood)

Internal osmotic pressure keeps the cell “inflated”

Hypertonic conditions:

cells dry and dye De cre asi ng sa lt

co nc en tra tio n

Incre asin

g salt

conc entra tion

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Application of Osmosis

• Using osmometry to determine molar mass of a macromolecule

Osmotic pressure is measured at a series of mass concentrations c and a plot of vs. c is used to determine molar mass.

/ c



[ ] B RT (1 b B [ ] ...)

   

 gh c M /

2 ...

h RT bRT

c   gM   gM c 

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