Acids and Bases

Chapter 15

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 Acidos

Sabor agrio vinagre tiene sabor a acetic acid. Citrus

fruits contain citric acid.
Reaccionan con ciertos metales y produce hydrogen
Reaccionan con carbonatos y bicarbonatos y producen dioxide
de carbono

Bases
Sabor amargo.
Se siente resbaladiza. varios jabones contienen bases.

4.3
Arrhenius: acido es la sustancia produce H+ (H3O+) en el agua

Arrhenius: base es la sustancia produce OH- en el agua

4.3
 Acido de Brønsted is donor de un proton
Base de Brønsted is un acceptor de proton

base acid acid base

conjugate conjugate
base acid
acid base

15.1
 Propiedades Acido-Base del agua

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

autoionization of water

+ -
H O + H O [H O H] + H O
H H H

conjugate
base
acid
H2O + H2O H3O+ + OH-
acid conjugate
base 15.2
 Producto de ionizacion del agua

[H+][OH-]
H2O (l) H+ (aq) + OH- (aq) Kc = [H2O] = constant
[H2O]

Kc[H2O] = Kw = [H+][OH-]

constante del product de ionizacion (Kw) es el producto de

las concentrations molares de H+ y OH- a una particular
temperatura.
Solution Is
[H+] = [OH-] neutral
At 250C [H+] > [OH-] acidic
+ -
Kw = [H ][OH ] = 1.0 x 10 - 14
[H+] < [OH-] basic

15.2
Cual es la concentracion de iones OH- en la solucion de
HCl 1.3 M?

Kw = [H+][OH-] = 1.0 x 10-14

[H+] = 1.3 M

K 1 x 10 -14
w -15 M
[OH-] = = = 7.7 x 10
[H+] 1.3

15.2
 pH – es una medida de Acidez

pH = -log [H+]

Solution Is At 250C
neutral [H+] = [OH-] [H+] = 1 x 10-7 pH = 7
acidic [H+] > [OH-] [H+] > 1 x 10-7 pH < 7
basic [H+] < [OH-] [H+] < 1 x 10-7 pH > 7

pH [H+]

15.3
 pOH = -log [OH-]

[H+][OH-] = Kw = 1.0 x 10-14

-log [H+] – log [OH-] = -14.00

pH + pOH = 14.00

15.3
El pH de agua de lluvia recogida en una region of the
northeastern United States en un day fue 4.82. cual es la
concentracion del ion H+ del agua de lluvia?

pH = -log [H+]
[H+] = 10-pH = 10-4.82 = 1.5 x 10-5 M

La concentracion de iones OH- en una muestra de sangre es

2.5 x 10-7 M. Cual es el pH de la sangre?
pH + pOH = 14.00
pOH = -log [OH-] = -log (2.5 x 10-7) = 6.60

pH = 14.00 – pOH = 14.00 – 6.60 = 7.40

15.3
 Electrolito fuerte – 100% disociacion
H 2O
NaCl (s) Na+ (aq) + Cl- (aq)

Electrolito debil – no se disocia completamente

CH3COOH CH3COO- (aq) + H+ (aq)

Acidos Fuertes son electrolitos fuertes

HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq)

HNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)
HClO4 (aq) + H2O (l) H3O+ (aq) + ClO4- (aq)
H2SO4 (aq) + H2O (l) H3O+ (aq) + HSO4- (aq)
15.4
Acids debiles son electrlitos debiles

HF (aq) + H2O (l) H3O+ (aq) + F- (aq)

HNO2 (aq) + H2O (l) H3O+ (aq) + NO2- (aq)
HSO4- (aq) + H2O (l) H3O+ (aq) + SO42- (aq)
H2O (l) + H2O (l) H3O+ (aq) + OH- (aq)

Bases Fuertes son electrolitos fuertes

H 2O
NaOH (s) Na+ (aq) + OH- (aq)
H 2O
KOH (s) K+ (aq) + OH- (aq)
H 2O
Ba(OH)2 (s) Ba2+ (aq) + 2OH- (aq)

15.4
Bases Debiles son electrolitos debiles

F- (aq) + H2O (l) OH- (aq) + HF (aq)

NO2- (aq) + H2O (l) OH- (aq) + HNO2 (aq)

Pares Conjugados acido-base :

• la base conjugada de un acido fuerte no tiene Fortaleza
medible.
• H3O+ es el acid mas fuerte que puede existir en una
solucion acuosa.
• OH- es la base mas fuerte que puede existir en solucion
acuosa.

15.4
15.4
Cual es el pH de una solucion de HNO3 2 x 10-3 M?
HNO3 acido fuerte – 100% disociado.
inicio 0.002 M 0.0 M 0.0 M
HNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)
final 0.0 M 0.002 M 0.002 M

pH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7

Cual es el pH de una solucion de Ba(OH)2 1.8 x 10-2 M s?

Ba(OH)2 base fuerte – 100% disociado.

inicio 0.018 M 0.0 M 0.0 M
Ba(OH)2 (s) Ba2+ (aq) + 2OH- (aq)
final 0.0 M 0.018 M 0.036 M
pH = 14.00 – pOH = 14.00 + log(0.036) = 12.6
15.4
Acido Debil (HA) y Constante de Ionizacion Acida

HA (aq) + H2O (l) H3O+ (aq) + A- (aq)

HA (aq) H+ (aq) + A- (aq)

[H+][A-]
Ka =
[HA]

Ka es la constant de ionization acida

weak acid
Ka
strength

15.5
15.5
 Cual es el pH de una solucion de HF 0.5 M ( 250C)?
[H+][F-]
HF (aq) H+ (aq) + F- (aq) Ka = = 7.1 x 10-4
[HF]
HF (aq) H+ (aq) + F- (aq)
Inicial (M) 0.50 0.00 0.00
Cambio (M) -x +x +x
Equilibrio (M) 0.50 - x x x
x2
Ka = = 7.1 x 10-4 Ka << 1 0.50 – x  0.50
0.50 - x
x2
Ka  = 7.1 x 10-4 x2 = 3.55 x 10-4 x = 0.019 M
0.50
[H+] = [F-] = 0.019 M pH = -log [H+] = 1.72
[HF] = 0.50 – x = 0.48 M
15.5
 Cuando usar la aproximacion?
Ka << 1 0.50 – x  0.50

cuando x es menor al 5% del valor del cual es sustraido.

0.019 M Less than 5%
x = 0.019 x 100% = 3.8%
0.50 M Approximation ok.

Cual es el pH de una solucion de HF 0.05 M (a 250C)?

x2
Ka  = 7.1 x 10-4 x = 0.006 M
0.05
0.006 M More than 5%
x 100% = 12%
0.05 M Approximation not ok.

solve for x exactly using quadratic equation or method of

successive approximation. 15.5
 Cual es el pH de un acido monoprotico 0.122 M para el cual
Ka is 5.7 x 10-4?
HA (aq) H+ (aq) + A- (aq)
Initial (M) 0.122 0.00 0.00
Change (M) -x +x +x
Equilibrium (M) 0.122 - x x x
x2
Ka = = 5.7 x 10-4 Ka << 1 0.122 – x  0.122
0.122 - x
x2
Ka  = 5.7 x 10-4 x2 = 6.95 x 10-5 x = 0.0083 M
0.122

0.0083 M More than 5%

x 100% = 6.8%
0.122 M Approximation not ok.

15.5
 x2
Ka = = 5.7 x 10-4 x2 + 0.00057x – 6.95 x 10-5 = 0
0.122 - x
-b ± b2 – 4ac
ax2 + bx + c =0 x=
2a
x = 0.0081 x = - 0.0081

HA (aq) H+ (aq) + A- (aq)

Initial (M) 0.122 0.00 0.00
Change (M) -x +x +x
Equilibrium (M) 0.122 - x x x

[H+] = x = 0.0081 M pH = -log[H+] = 2.09

15.5
 concentracion en equilibrio del acido Ionized
% ionizacion = x 100%
Concentracion inicial del acido

For a monoprotic acid HA

[H+]
% ionizacion = x 100% Donde [HA]0 = initial concentration
[HA]0

15.5
Base Debil y Constante de Ionizacion de la Base

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

[NH4+][OH-]
Kb =
[NH3]

Kb is the base ionization constant

weak base
Kb
strength

pOH + pH = 14

15.6
15.6
Constantes de ionizacion de Pares Conjugados Acid-Base

HA (aq) H+ (aq) + A- (aq) Ka

A- (aq) + H2O (l) OH- (aq) + HA (aq) Kb

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

KaKb = Kw

Acido debil y su base Conjugada

Kw Kw
Ka = Kb =
Kb Ka

15.7
15.8
 Estructura molecula y magnitud acida
H X H+ + X-

The The
stronger weaker
the bond the acid

HF << HCl < HBr < HI

15.9
 Molecular Structure and Acid Strength

2. Oxiacidos con el atomo central comun (Z) pero diferente

numero de grupos enlazados.

La fuerza acida aumenta si el numero de oxidacion de Z aumenta

HClO4 > HClO3 > HClO2 > HClO

15.9
 Propiedades Acido-Base de las sales
Soluciones Neutras:
Salts containing an alkali metal or alkaline earth metal
ion (except Be2+) and the conjugate base of a strong
acid (e.g. Cl-, Br-, and NO3-).
H2O
NaCl (s) Na+ (aq) + Cl- (aq)

Soluciones Basicas:
Salts derived from a strong base and a weak acid.
H 2O
NaCH3COOH (s) Na+ (aq) + CH3COO- (aq)

CH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)

15.10
 Propiedades Acido-Base de las sales
Soluciones Acidas:
Salts derived from a strong acid and a weak base.

H2O
NH4Cl (s) NH4+ (aq) + Cl- (aq)

NH4+ (aq) NH3 (aq) + H+ (aq)

Salts with small, highly charged metal cations (e.g. Al3+,

Cr3+, and Be2+) and the conjugate base of a strong acid.

Al(H2O)3+
6 (aq) Al(OH)(H2O)52+(aq) + H+ (aq)

15.10
Acid Hydrolysis of Al3+

15.10
 Acid-Base Properties of Salts
Solutions in which both the cation and the anion hydrolyze:

• Kb for the anion > Ka for the cation, solution will be basic
• Kb for the anion < Ka for the cation, solution will be acidic
• Kb for the anion  Ka for the cation, solution will be neutral

15.10
Oxides of the Representative Elements
In Their Highest Oxidation States

CO2 (g) + H2O (l) H2CO3 (aq)

N2O5 (g) + H2O (l) 2HNO3 (aq)

15.11
 Definition of An Acid
Arrhenius acid is a substance that produces H+ (H3O+) in water

A Brønsted acid is a proton donor

A Lewis acid is a substance that can accept a pair of electrons

A Lewis base is a substance that can donate a pair of electrons

•• ••
H+ + OH-
••
H O H
•• ••
acid base
H H
+
H+ +
••

N H H N H
H H
acid base
15.12
 Lewis Acids and Bases

F H F H
F B + F B

••
N H N H
F H F H
acid base

No protons donated or accepted!

15.12