Chapter 15.6, Problem 1RCF

Interpretation Introduction

Interpretation:

The $pH$ of a $0.055M$ solution of an unknown weak base with $K_{b}of9.1\times {10}^{-8}$ has to be determined.

Concept Information:

Base ionization constant ${\text{K}}_{\text{b}}$:

It is the equilibrium constant for the ionization of a base.

The ionization of a weak base $B$ is,

${\text{B}}_{\left(\text{aq}\right)}\text{+}{\text{H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}\rightleftarrows {\text{BH}}_{\left(\text{aq}\right)}^{\text{+}}\text{+}{\text{OH}}_{\left(\text{aq}\right)}^{\text{-}}$

The equilibrium expression for the above reaction is given below.

${\text{K}}_{\text{b}}\text{=}\frac{{\text{[BH}}^{\text{+}}{\text{][OH}}^{\text{-}}\text{]}}{\text{[B]}}$

$pOH$  of a solution is the negative logarithm of the molar concentration of hydroxide ion concentration.

$\text{pOH}\text{=}\text{-log}\left[{\text{OH}}^{\text{-}}\right]$

Concentration of hydronium ion $\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\right]\text{=}{\text{10}}^{\text{-pH}}$

pH of a solution is the negative of the base $\text{-10}$ logarithm of the hydronium ion or hydrogen ion concentration.

$\text{pH}\text{=}\text{-log}\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\right]$

$pH+pOH=14$

ICE (reaction initial concentration equilibrium) table is mainly used to calculate the value of K for a reaction. This table contains the concentration of reactant and product in various stage of reaction.