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Sumario Tema 7 - Ácidos y bases $3.70
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Sumario Tema 7 - Ácidos y bases

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1. Definiciones generales 2. Disolución del agua 3. Cálculo del pH y del pOH 4. Fuerzas de ácidos y bases 5. Constantes de disociación 6. Hidrólisis 7. Valor de las acciones ácido - base

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  • January 7, 2025
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QUÍMICA TEMA 7




TEMA 7
ÁCIDOS Y BASES

7.1 – DEFINICIONES GENERALES
ARRHENIUS:
Ácido: Toda sustancia que cede iones H+ al disolverse en agua.
HA ⟷ A– + H+ → HNO2 ⟷ NO$
# +H
+


Base: Se dice de la sustancia que cede iones OH– al disolverla en agua.
MOH ⟷ M+ + OH– → NH4OH ⟶ NH)* + OH–

Los ácidos y las bases se pueden neutralizar:
neutralizar
HA + MOH ⟶ MA + H2O (H+ + H2O ⟶ H2O)

BRØN
BRØNSTED
ØNSTED Y LOW
LOWRY:
Ácido: Toda sustancia capaz de ceder protones (A).
Base: Toda sustancia capaz de captar
captar protones (B).
HA ⟷ A– + H+ B + H+ ⟷ HB+
Ácido Base conjugada Base Ácido conjugado


Ácido + Base ⟷ Base conjugada + Ácido conjugado:
conjugado
HNO2 + H2O ⟷ NO– + H3O+
NH3 + H2 ⟷ NH)* + OH–

ANFÓTERO: Sustancia que puede actuar como ácido y como base dependiendo de con quien actúe.

7.2 – DISOLUCIÓN DEL AGUA
ARRHENIUS: H2O ⟷ H+ + OH– ⟶ Kw = [H+] · [OH–] (El agua es líquido que no se tiene en cuenta).

BRØNSTED Y LOWRY:
LOWRY: H2O + H2O ⟷ H3O+ + OH– ⟶ Kw = [H3O+] · [OH–]

Kw → Producto iónico del agua o constante de equilibrio de disociación del agua.
El valor de Kw a 25ºC es de 1 · 10-14
• [H3O+] = [OH–] = 1 · 10-7 M
• [H+] = [OH–] = 1 · 10-7 M

, QUÍMICA TEMA 7



La acidez de una disolución de representa mediante la concentración de hidronio (H3O+).
Disolución neutra: Sucede cuando no se altera el equilibrio de disociación del agua.
[H3O+] = 1 · 10-7 M
Disoluciones ácidas: Contienen más hidronios que los que contiene el agua pura.
[H3O+] > 1 · 10-7 M
Disoluciones básicas: Contienen menos hidronios que el agua pura.
[H3O+] < 1 · 10-7 M


7.3 – CÁLCULO DEL pH Y DEL pOH
pH = – log [H3O+] = – log [H+]
pH + pOH = 14
pOH = 1 – log [OH–]

ESCALA DEL PH SEGÚN BRØNSTED Y LOWRY:
LOWRY:
H2O + H2O ⟷ H3O+ + OH– ⟶ Kw = 1 · 10-14

Si [H3O+] = 1 ⟶ [OH–] = 1 · 10-14 ⟶ pH = 0 pOH = 14
Si [H3O+] = 1 · 10-7 ⟶ [OH–] = 1 · 10-7 ⟶ pH = 7 pOH = 7
Si [H3O+] = 1 · 10-14 ⟶ [OH–] = 1 ⟶ pH = 14 pOH = 0

Disoluciones ácidas → 0 < pH < 7
Disoluciones básicas → 7 < pH < 14


7.4 – FUERZAS DE ÁCIDOS Y BASES
ARRH
ARRHENIUS:
Un ácido fuerte es el que está totalmente disociado.
disociado Del mismo modo una base fuerte es la que se
encuentra totalmente disociada.
disociada
Un ácido débil está parcialmente disociado y una base débil está parcialmente disociada.
disociada
Ácidos fuertes: HCl, HBr, HI, HNO3, HClO4, H2SO4.
Bases fuertes: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2.

ÁCIDOS:
Arrh
Arrhenius: HCl ⟶ Cl– + H+
Brønsted y Lowry:
Lowry: HCl + H2O ⟷ Cl– + H3O+

BASES:
Arrh
Arrhenius: NaOH ⟶ Na+ + OH–
Brønsted y Lowry:
Lowry: NaOH ⟷ (NaOH2)+ + OH–

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