Textbook Problem

What is meant by the presence of a common ion? How does the presence of a common ion affect an equilibrium such as

HNO₂(aq) ⇌ H⁺(aq) + NO₂^-(aq)

What is an acid–base solution called that contains a common ion?

Interpretation Introduction

Interpretation:

The presence of a common ion is to be explained. The affect of the presence of a common ion on equilibrium of the given reaction is to be stated. The term used for an acid-base solution that contains a common ion is to be determined.

Concept introduction:

The presence of a common ion brings about a shift in the equilibrium position.

To determine: An explanation regarding the presence of a common ion.

Answer to Problem 1RQ

The presence of a common ion shifts the equilibrium position.

Explanation of Solution

The shift in the equilibrium state that happens due to the addition of an ion that is already present in the equilibrium reaction is stated as the presence of a common ion.

Interpretation Introduction

Interpretation:

The presence of a common ion is to be explained. The affect of the presence of a common ion on equilibrium of the given reaction is to be stated. The term used for an acid-base solution that contains a common ion is to be determined.

Concept introduction:

The presence of a common ion brings about a shift in the equilibrium position.

To determine: The affect of the presence of a common ion on equilibrium of the given reaction

Answer to Problem 1RQ

The presence of a common ion shifts the equilibrium of the given reaction towards left.

Explanation of Solution

The given reaction is,

${\text{HNO}}_2{}_{\left(\text{aq}\right)}\rightleftharpoons {\text{H}}^{+}{}_{\left(\text{aq}\right)}+{\text{NO}}_2^{-}{}_{\left(\text{aq}\right)}$

The presence of a common ion in the given reaction will reduce the solubility of the given acid shifting the equilibrium towards the left. The dissociation of the given acid will be suppressed.

Interpretation Introduction

Interpretation:

The presence of a common ion is to be explained. The affect of the presence of a common ion on equilibrium of the given reaction is to be stated. The term used for an acid-base solution that contains a common ion is to be determined.

Concept introduction:

The presence of a common ion brings about a shift in the equilibrium position.

To determine: The term used for an acid-base solution that contains a common ion.

Answer to Problem 1RQ

An acid-base solution that contains a common ion is a buffer solution.

Explanation of Solution

An acid-base solution that contains a common ion is a buffer solution.

A buffer solution is also defined as a solution that resists a change in the $\text{pH}$ on addition of an acid or an alkali

Conclusion

A solution that resists a change in the $\text{pH}$ on addition of an acid or an alkali is termed as a buffer solution