Chapter 19, Problem 95A

Interpretation Introduction

Interpretation : The solutions are to be arranged in order of decreasing acidity.

Concept Introduction : Acids are substances that contain hydrogen and ionize to produce hydrogen ions $\left({\text{H}}^{\text{+}}\right)$ in an aqueous solution.

Answer to Problem 95A

The solutions are arranged in order of decreasing acidity is given below:

  $0.1\text{M}\text{HCl}\left(\text{b}\right)\text{>}0.1\text{M}{\text{NH}}_4\text{Cl}\left(\text{c}\right)>\text{0}\text{.1}\text{M}{\text{CH}}_{\text{3}}\text{COONa}\left(\text{d}\right)\text{>}0.1\text{M}\text{NaOH}\left(\text{a}\right)$

Explanation of Solution

Consider $0.1\text{M}\text{NaOH}$ solution.

Since sodium hydroxide is a strong base and entirely dissolves in water, the pH rises, reducing the acidity of the sodium hydroxide solution.

Consider $0.1\text{M}\text{HCl}$ solution.

Since hydrochloric acid is a strong acid and dissociates into cation and anion thereby increasing the hydrogen ion and so the pH drops. So, this is the strongest acid.

Consider $0.1\text{M}{\text{NH}}_4\text{Cl}$ solution.

The salt known as ammonium chloride is made up of an anion from a strong acid and a cation from a weak base. So, it is the second strongest acid.

Consider $\text{0}\text{.1}\text{M}{\text{CH}}_{\text{3}}\text{COONa}$ solution.

An anion of a weak acid and a cation of a strong base make up sodium ethanoate.

This is third strongest acid.

So, the order of decreasing acidity is as follows:

  $0.1\text{M}\text{HCl}\text{>}0.1\text{M}{\text{NH}}_4\text{Cl}>\text{0}\text{.1}\text{M}{\text{CH}}_{\text{3}}\text{COONa}\text{>}0.1\text{M}\text{NaOH}$