Chapter 21, Problem 7E

Interpretation Introduction

(a)

Interpretation:

To calculate $\text{pH}$ of the solution after electrolysis.

Concept introduction:

The relation between current, charge and time is,

$Q=It$

Where, Q is charge, I is current and t is time.

Concentration can be calculated from the following formula,

$\text{Concentration=}\frac{\text{Moles}}{\text{Volume}\text{of}\text{solution}}$

Negative logarithm of hydrogen ion concentration is $\text{pH}$.

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

Interpretation Introduction

(b)

Interpretation:

To determine why pH does not depend on the initial concentration of KCl.

Concept introduction:

In electrolysis two reaction occurs that is, on at anode and one at cathode. For $\text{KCl}$ solution undergoing electrolysis the reaction are,

$\begin{array}{l}\text{Cathode}\text{:}{\text{2H}}_2\text{O}+2e^{-}\to {\text{H}}_{\text{2}}+2{\text{OH}}^{-}\\ \text{Anode}\text{:}{\text{2Cl}}^{-}\to {\text{Cl}}_2+2e^{-}\end{array}$

If hydroxide ion concentration is known in a solution, then pH of solution can be determined easily from ionic product of water concentration.