Chapter 6, Problem 6C.7E

Interpretation Introduction

Interpretation:

The order of increasing strength of given acids ${\text{HCOOH, (CH}}_{\text{3}}{\text{)}}_{\text{3}}{\text{NH}}^{\text{+}}{\text{, N}}_{\text{2}}{\text{H}}_{\text{5}}{}^{\text{+}}\text{, HF}$ has to be arranged.

Concept Introduction:

The strength of proton donating of an acid is called acidity constant and also the acidity constant is said to be as their negative logarithms and which can be represented as follows,

    ${\text{pK}}_{\text{a}}\text{=}{\text{-logK}}_{\text{a}}$

When looking for the strength of acids and bases the following points should be noted,

• Weak acid always have the smaller value of ${\text{K}}_{\text{a}}$ and has greater value of ${\text{pK}}_{\text{a}}\text{.}$
• Weak base always have the smaller value of ${\text{K}}_{\text{b}}$ and has greater value of ${\text{pK}}_{\text{b}}\text{.}$

Generally acid donates proton to form conjugate base.  As donation of proton takes place, the conjugate base will have fewer hydrogen ions than that is present in acid.  Base accepts protons to form conjugate acid.  As proton is accepted, the conjugate acid will have more hydrogen ions than that of the base from which it is formed.

Sum of acidity constant and basicity constant is equal to $14.00$.  $K_a$ is the acidity constant of acid while $K_b$ is the basicity constant of base.  The equation can be given as shown below;

    $\text{p}{K}_a+\text{p}{K}_b=\text{p}{K}_w$