Acid/Base

Arrhenius definition acid produces H+ in water

base produces OH- in water

HA

Ka = [H+] [A-]

[HA] [H2O]

Ka strength of acid

strong acids

dissociate completely

no Ka

HCl,

HNO3,

weak acids

equilibrium process

HF

+ H2O H++ A-

[HA]

HBr, HI

HClO4, H2SO4

Ka = 6.8 x 10-4

HIO3 Ka = 0.16

Acid/Base

Arrhenius definition acid produces H+ in water

base produces OH- in water

strong bases

O2-

OH- Group I

Group II

(Ca, Sr, Ba)

weak bases

NH3

R-NH2

NaOH (s) + H2O Na+(aq)

NH3 (g) + H2O NH4+ (aq) + OH- (aq)

+ OH- (aq)

Kb

amines

Kb = 1.8 x 10-5

Brønsted-Lowry Acids and Bases

acid proton donor

base proton acceptor

H Cl + OH

H

.. .. Cl- +..OH

H

H+

acidbase acid

baseconjugate pair

conjugate pair

very weakstrong

H..

stronger acid + stronger base

Brønsted-Lowry Acids and Bases

strength of acid related to stability of conjugate base

conjugate bases carry negative charges

stabilized by: polarizability

electronegativity

inductive effect

resonance

related to size (LDF)

HI H+ + I-

HBr H+ + Br-

HCl H+ + Cl-

HF H+ + F-

e- in

5p orbital4p orbital3p orbital2p orbital

largest orbitalmost stable

strongest acid

Brønsted-Lowry Acids and Bases

strength of acid related to stability of conjugate base

conjugate bases carry negative charges

stabilized by: electronegativity

with same size orbitals, electronegativity determines stability

F- OH- NH2- CH3

-

HF > H2O NH3 CH4> >

Brønsted-Lowry Acids and Bases

strength of acid related to stability of conjugate base

conjugate bases carry negative charges

inductive effect

related to electronegativity – but atom near charge

stronger acid

more stable base

Brønsted-Lowry Acids and Bases

strength of acid related to stability of conjugate base

conjugate bases carry negative charges

resonance

HNO3 HNO2

For oxoacids with same central atom,more O means stronger acid

For oxoacids with same number of O,more electronegative central atom means stronger acid

Brønsted-Lowry Acids and Bases

acid proton donor

base proton acceptor

NH H

H

..+ OH

H

.. .. NH H

H

H+

+

..

..OH

..-

base

acid

acid

base

weak base relatively strong acidKb

= 1.8 x 10-5

Autoionization of H2O

H2O H+ (aq) + OH- (aq)

Kw = [H+] [OH-]

[H2O]

= 1.0 x 10-14 at 25oC

55.5 M- 0.0000001

Le Chatelier add H+ [OH-] decrease

0.10 mol HCl1.0 L

= 0.1 mol H+

L[H+] = 0.10 M

[H+] = [OH-] = 1.0 x 10-7

Kw = [0.1] [OH-] = 1.0 x 10-14

[OH-] = 1.0 x 10-13

both present in all aqueous solutions

H 0>

pH[H+] 10 M - 10-15 M pH = - log [H+]

-1pH 15low

acidic

high pHbasic

[H+] = [OH-]= 1.0 x 10-7 pH = 7neutral

pOH = - log [OH-]pH + pOH = 14

pH of milk = 6.4 [H+] =10 -6.4

3.981071706 x 10-7

1 sig. fig.

4 x 10-7

Brønsted-Lowry Acids and Bases

acid proton donor

base proton acceptor

+C2H3OOH CN- C2H3OO- + HCNacid base1base acid2

1 2

Brønsted-Lowry Acids and Bases

acid proton donor

base proton acceptor

HF + H2O F- + H3O+

acid1 base1base2 acid2

H3O+ strongest acid in water

CH3NH2 + H2O CH3NH3+ + OH-

base1 acid2 acid1 base2

OH- strongest base in wateramphoteric

acid or baseH2O

Ka = 7.2 x 10-4