ch 2. polarite-solubilite acides et bases .1. acides et bases ch 2. polarite-solubilite acides et

CH 2. POLARITE-SOLUBILITE ACIDES ET BASES

PROPRIETES PHYSIQUES

1. Acides et Bases

CH 2. POLARITE-SOLUBILITE ACIDES ET BASES

PROPRIETES PHYSIQUES

Dfinitions et notions Force des acides et bases Position de lquilibre Neutralisation Neutralisation et pH

ARRHENIUS

Acide = donneur de H+ Base = donneur de OH-

HCl + NaOH NaCl + HOH

HCl + NH3 NH4+ Cl- ?????

BROENSTED-LOWRY:

Toute raction dans laquelle on change un H+ est une raction acide-base

Acide : fournit H+ une base Base : accepte H+ dun acide

Les bases, charges ou non, fixent le proton par une paire libre dlectrons

H-Cl + NH3 NH4+ Cl- ?????

A-H + :B A- + B-H+

acide base base acide conjugue conjugu

H-Cl + NH3 NH4+ Cl-

!!! La notion dacide et de base est relative :

Acide Base Base Acide conjugue conjugu

Acide Base Base Acide conjugue conjugu

H3O+ + OH- H2O + H2O

Acide Base Base Acide conjugue conjugu

H3O+ + OH- H2O + H2O

H2O + H2O OH- + H3O+

Acide Base Base Acide conjugue conjugu

H3O+ + OH- H2O + H2O

H2O + H2O OH- + H3O+

CH3OH + CH3OH CH3O- + CH3OH2+

Acide Base Base Acide conjugue conjugu

H3O+ + OH- H2O + H2O

H2O + H2O OH- + H3O+

CH3OH + CH3OH CH3O- + CH3OH2+

NH4+ + NH2- NH3 + NH3

Acide Base Base Acide conjugue conjugu

H3O+ + OH- H2O + H2O

H2O + H2O OH- + H3O+

CH3OH + CH3OH CH3O- + CH3OH2+

NH4+ + NH2- NH3 + NH3

H2S + OH- HS- + H2O

Force des acides et des bases :

HA + H2OKa

A- H3O++

Si la force de l'acide augmente : Ka augmente et pKa (= - log Ka) diminue

Ka = [H3O+] [A-]

[HA]

Les repres importants pour la chimie organique: Acide Formule pKa Base

conjugueAcide Formule pKa Base

conjugue

Acide actique CH3COOH 4.75 CH3COO-

Phnol C6H5OH 10.00 C6H5O-

Eau H2O 15.70 OH-

Acide Formule pKa Baseconjugue

Acide phosphorique H3PO4 2.10 H2PO4-

Acide benzoque C6H5COOH 4.20 C6H5COO-

Acide actique CH3COOH 4.75 CH3COO-

Acide carbonique H2CO3 6.40 HCO3-

Dihydrognophosphate H2PO4- 7.20 HPO4

- -

Ammonium NH4+ 9.20 NH3

Methylammonium CH3NH3+ 9.60 CH3NH2

Phnol C6H5OH 10.00 C6H5O-

Bicarbonate HCO3- 10.30 CO3

- -

Hydrognophosphate HPO4- - 12.30 PO4

- - -

Eau H2O 15.70 OH-

Ethanol C2H5OH 15.90 C2H5O-

Acides trs forts (par ordre dacidit dcroissante) :

Acides trs faibles (par ordre dacidit dcroissante) :

Acide Formule Baseconjugue

Acide chlorhydrique HCl Cl-

Acide sulfurique H2SO4 HSO4-

Hydronium H3O+ H2O

Acide Formule Baseconjugue

Actylne

Hydrogne H2 H-

Ammoniac NH3 NH2-

Ethane CH3CH3 CH3CH2-

HC CH HC C-

Kq

pKa = 9.31= 4.75 pKa

Acide cyanhydriqueAcide actique

+CH3CO2-

CN-

+ HCNCH3CO2H

.

Position de lquilibre acide-base

= 3.55 104

[ ][ ]

[ ][ ]

=CNHCN

COOHCHCOOCHK

3

3eq

[ ][ ]

[ ][ ]

[ ][ ]+

+

=OHOH

CNHCN

COOHCHCOOCHK

3

3

3

3eq

[ ][ ]

[ ][ ]

[ ][ ] HCNa

COOHCHa

3

3

3

3eq K

KOHOH

CNHCN

COOHCHCOOCHK

3

==+

+

Position de lquilibre acide-base

Si Keq > 102

Si Keq < 10-2

Equilibre dplac droite : La raction est une neutralisation

Equilibre dplac gauche Pas de raction

Si 10-2 < Keq < 102 Un quilibre stablit Raction incomplte

Neutralisation

H2O+ OH- A- +

Acide EaupKa= 4 = 15.7pKa

KqA-H

CA-H = [A-H] + [A-] .

Kq = 1011.7

f A-H = [A-H] / CA-H .Fraction non dissocie f A- = [A-] / CA-H .Fraction dissocie

CA-H = [A-H] + [A-] .f A-H = [A-H] / CA-H .

f A- = [A-] / CA-H .!!! Aucune information sur le pH !!!

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

1.40 0.60 0.60 0.60 0.700 0.300 0.300Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

1.40 0.60 0.60 0.60 0.700 0.300 0.300

1.00 1.00 1.00 1.00 0.500 0.500 0.500Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

1.40 0.60 0.60 0.60 0.700 0.300 0.300

1.00 1.00 1.00 1.00 0.500 0.500 0.500

0.60 1.40 1.40 1.40 0.300 0.700 0.700

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

1.40 0.60 0.60 0.60 0.700 0.300 0.300

1.00 1.00 1.00 1.00 0.500 0.500 0.500

0.60 1.40 1.40 1.40 0.300 0.700 0.700

0.20 1.80 1.80 1.80 0.100 0.900 0.900

0.05 1.95 1.95 1.95 0.025 0.975 0.975

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

[A-H] + [B] [A- ] + [HB+] f A-H f A- Eqv B

2.00 0.00 0.00 0.00 1.000 0.000 0.000

1.95 0.05 0.05 0.05 0.975 0.025 0.025

1.80 0.20 0.20 0.20 0.900 0.100 0.100

1.40 0.60 0.60 0.60 0.700 0.300 0.300

1.00 1.00 1.00 1.00 0.500 0.500 0.500

0.60 1.40 1.40 1.40 0.300 0.700 0.700

0.20 1.80 1.80 1.80 0.100 0.900 0.900

0.05 1.95 1.95 1.95 0.025 0.975 0.975

0.00 2.00 2.00 2.00 0.000 1.000 1.000

Neutralisation et pH

[ ][ ][ ]HA

AOHK 3OHa 2+

=

[ ] [ ][ ]!

!"

#$$%

&+=

+

HAAlogOHlogKlog 3a

[ ][ ]!

!"

#$$%

&+=

HAAlogpKpH a

Equation de HENDERSON-HASSELBALCH

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

Neutralisation d'un acide

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

pH

[A-H] + [B] [A- ] + [HB+] Eqv B pH log([A-]/[A-H]) [A-]/[A-H]

2.00 0.00 0.00 0.00 0.000

1.95 0.05 0.05 0.05 0.025 2.41 -1.591 0.026

1.80 0.20 0.20 0.20 0.100 3.05 -0.954 0.111

[ ][ ]!

!"

#$$%

&+=

HAAlogpKpH a

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

Neutralisation d'un acide

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

pH

[A-H] + [B] [A- ] + [HB+] Eqv B pH log([A-]/[A-H]) [A-]/[A-H]

2.00 0.00 0.00 0.00 0.000

1.95 0.05 0.05 0.05 0.025 2.41 -1.591 0.026

1.80 0.20 0.20 0.20 0.100 3.05 -0.954 0.111

1.40 0.60 0.60 0.60 0.300 3.63 -0.368 0.429

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

Neutralisation d'un acide

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

pH

[A-H] + [B] [A- ] + [HB+] Eqv B pH log([A-]/[A-H]) [A-]/[A-H]

2.00 0.00 0.00 0.00 0.000

1.95 0.05 0.05 0.05 0.025 2.41 -1.591 0.026

1.80 0.20 0.20 0.20 0.100 3.05 -0.954 0.111

1.40 0.60 0.60 0.60 0.300 3.63 -0.368 0.429

1.00 1.00 1.00 1.00 0.500 4.00 0.000 1.000

Neutralisation d'un acide

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

f

Neutralisation d'un acide

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00

Equivalents de base

pH

[A-H] + [B]