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  • 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]

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