Chapter 14.6, Problem 43PP

Interpretation Introduction

Interpretation: “The neutral solution has a $pHof7$ ”should be explained

Concept Introduction:

• $pH$ of a solution is defined as the negative logarithm of the hydrogen ion concentration of the aqueous solution.

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

• Water is a very weak conductor of electricity. This suggests that it undergoes self-ionization to a very small extent. Due to self ionization, the following equilibrium is set up between water and its ions.

  $H_2{O}_{(l)}+H_2{O}_{(l)}\leftrightarrow H^{+}{}_{(aq)}+O{H}^{-}{}_{(aq)}$

Applying law of mass action, the equilibrium constant $K_c$ for the self ionization of water can be written as

  

Since degree of ionization of water is very low, its ionization does not appreciably changes the concentration of water molecules. Therefore ${\left[H_{2}O\right]}^2$ may be regarded as constant.

  $K_{c}K=\left[H^{+}\right]\left[O{H}^{-}\right]$

where $K$ is a constant representing ${\left[H_{2}O\right]}^2$

Now,

  $K_w=\left[H^{+}\right]\left[O{H}^{-}\right]$

Where $K_w$ is the product of two constant $K_{c}andK$

  $K_w$ is called the ionic product of water and its value is $1\times 10^{-14}$