Chapter 16, Problem 16.41QP

Interpretation Introduction

Interpretation:

From the given concentration of $\text{HCN}$, the concentrations of ${\text{H}}^{\text{+}}{\text{,CN}}^{\text{-}}\text{and}{\text{OH}}^{\text{-}}$ ions have to be calculated.

Concept Introduction:

Approach to the problem:

With the ${\text{K}}_{\text{a}}$ value of $\text{HCN}$ and using ICE table, the value of ${\text{CN}}^{\text{-}}$ and ${\text{H}}_3{\text{O}}^{+}$ ions can be calculated. From the concentration of the ${\text{H}}_3{\text{O}}^{+}$ ion, the $\text{pOH}$ can be calculated. From the $\text{pOH}$, the concentration of ${\text{OH}}^{-}$ ion can be calculated.

If the value of $\text{pOH}$ has been given then the concentration of ${\text{OH}}^{-}$ ion can be calculated as follows:

  $\begin{array}{l}\text{pOH}\text{=}-{\log }_{10}\left[{\text{OH}}^{-}\right]\\ \left[{\text{OH}}^{-}\right]={10}^{\text{-pOH}}\end{array}$

$pHandpOH$ can be related as follows:

  $\begin{array}{l}pH+pOH=14\\ pH=14-pOH\\ pOH=14-pH\end{array}$

$\text{pH}$ is the negative logarithm of concentration of ${\text{H}}^{\text{+}}$ ion in a solution.

It can be expressed as

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

ICE table is used to determine the equilibrium concentration of any chemical species under dynamic equilibrium. ICE is the abbreviation of the words “Initial Change and Equilibrium”. The ICE table tabulates the following criteria:

• Initial concentration
• Change in the concentration
• Concentration at equilibrium or final concentration.

The equilibrium concentration of any species has to be taken into concentration for its concentration in calculation.