T6: Equilibrios acido-base · Teoría de Brönsted-Lowry — QUIMICA PEvAU Andaluc%252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525C3%252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525ADa 2018

Teoría de Brönsted-Lowry

Teoría

2018 · Extraordinaria · Suplente

Aplicando la teoría de Brönsted-Lowry para ácidos y bases, y teniendo en cuenta que el ácido cloroso ( $\ce{HClO2}$ ) es un ácido débil ( $K_a = 1,1 \cdot 10^{-2}$ ):

a) Escriba la reacción química del agua con el ácido cloroso y la expresión de su constante de acidez.b) Escriba la reacción química del agua con la base conjugada del ácido y la expresión de su constante de basicidad.c) Obtenga el valor de la constante de basicidad de su base conjugada.

Brönsted-LowryÁcido débilConstante de basicidad

a) El ácido cloroso,

\ce{HClO2}

, reacciona con el agua cediendo un protón, actuando como ácido de Brønsted-Lowry. El agua actúa como base.

\ce{HClO2(aq) + H2O(l) <=> ClO2-(aq) + H3O+(aq)}

La expresión de la constante de acidez ( $K_a$ ) para esta reacción es:

K_a = \frac{[\ce{ClO2-}][\ce{H3O+}]}{[\ce{HClO2}]}

b) La base conjugada del ácido cloroso (

\ce{HClO2}

) es el ion clorito (

\ce{ClO2-}

). Esta base conjugada reacciona con el agua aceptando un protón del agua.

\ce{ClO2-(aq) + H2O(l) <=> HClO2(aq) + OH-(aq)}

La expresión de la constante de basicidad ( $K_b$ ) para esta reacción es:

K_b = \frac{[\ce{HClO2}][\ce{OH-}]}{[\ce{ClO2-}]}

c) La relación entre la constante de acidez de un ácido débil (

K_a

) y la constante de basicidad de su base conjugada (

K_b

) se establece mediante el producto iónico del agua (

K_w

K_a \cdot K_b = K_w

Dado que $K_a = 1,1 \cdot 10^{-2}$ y $K_w = 1,0 \cdot 10^{-14}$ (a 25 °C), se puede calcular $K_b$ :

K_b = \frac{K_w}{K_a} = \frac{1,0 \cdot 10^{-14}}{1,1 \cdot 10^{-2}}

K_b \approx 9,1 \cdot 10^{-13}