Chapter 16, Problem 16.122SP

(a)

Interpretation Introduction

Interpretation:

The net ionic equation should be written for the reaction between iron oxide and $HCl$.  Also the Bronsted acid and Bronsted base in the reaction has to be identified.

Concept Information:

Bronsted's definitions of acid and base:

Bronsted's definition is based on the chemical reactions that occur when both acids and bases are added with each other. In Bronsted's theory acid donates proton, while base accepts proton from acid resulting in the formation of water.

Example: Consider the following reaction.

    $\text{HCl}\text{+}{\text{NH}}_{\text{3}}\to {\text{NH}}_{\text{4}}{}^{\text{+}}\text{+}{\text{Cl}}^{\text{-}}$

Hydrogen chloride donates a proton, and hence it is a Bronsted acid. Ammonia accepts a proton, and hence it is a Bronsted base.

(b)

Interpretation Introduction

Interpretation:

The net ionic equation for the two stage reaction of $CaC{O}_3$ with $HCl$ has to be written.

Concept Information:

Strong acids:

In strong acids, the ionization of acid is complete.  This implies that the concentration of the hydrogen ion or hydronium ion will be equal to the initial concentration of the acid at equilibrium.

Weak acids:

In weak acids, the ionization of acid is not complete.  This implies that the concentration of the hydrogen ion or hydronium ion will not  be equal to the initial concentration of the acid at equilibrium.

For strong acids the concentration of acid will be same as that of the concentration of hydrogen ions, because strong acids undergo complete ionization.

In case of weak acid, the concentration of hydrogen ion will be less than the concentration of given acid; since weak acid does not ionize completely.

(c)

Interpretation Introduction

Interpretation:

The $pH$ has to be calculated for the given acid solution.

Concept Information:

pH definition:

The acidity of aqueous solution is expressed by $\text{pH}$ scale.

The concentration of hydrogen ion in an aqueous solution is measured using $\text{pH}$ scale.

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

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

pH scale:

The acidity or basicity of an aqueous solution was called using a numerical scale called pH scale.

Based on pH of the solution, salt solutions can be classified as

• Acidic        -    (pH will be less than seven)
• Basic         -    (pH will be more than seven)
• Neutral     -    (pH will be equal to seven)

When both the cation and the anion react with water, the pH of the solution will depend on the relative magnitudes of ${\text{K}}_{\text{a}}$ for the cation and ${\text{K}}_{\text{b}}$ for the anion.