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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