Chapter 3, Problem 70CP

(a)

Interpretation Introduction

Interpretation:

Among the following, the compound that is not more acidic than Water has to be identified.

Concept Introduction:

Curved arrows: Curved arrows are used to show the direction of electrons movement. It has a tail (the source of electrons, usually lone pair or bonding pair from a sigma or pi-bond) and head (the destination of electrons, usually forming new lone pair on atom or a new bond). Electrons always flow from high electron density to low electron density.

Conjugate base stability: As the acid deprotonates, the stability of conjugate base formed is analyzed on the basis of electronegativity.

(b)

Interpretation Introduction

Interpretation:

The position of equilibrium for the given reaction has to be predicted.

Concept Introduction:

Predicting position of equilibrium: By comparing the conjugate bases using their structures, the position of equilibrium can be predicted. The equilibrium favors towards the most stabilized negative charge of conjugate base.

For example: $\text{H}-\text{A}\text{+}{\text{B}}^{\text{-}}\rightleftharpoons {\text{A}}^{\text{-}}\text{+}\text{H}-\text{B}$

In the above reaction if ${\text{B}}^{\text{-}}$ conjugate base is more stable, then equilibrium will favors formation of ${\text{B}}^{\text{-}}$. If ${\text{A}}^{\text{-}}$ is more stable, then equilibrium will favor for formation of ${\text{A}}^{\text{-}}$ Hence, the position of equilibrium can be predicted by comparing the stability of ${\text{A}}^{\text{-}}$ and ${\text{B}}^{\text{-}}$.

Using $p{K}_a$values to compare Acidity: In general, acid-base reaction said to reach equilibrium; the position of equilibrium is described by the term $K_{eq}$. When an acid-base reaction is carried out in aqueous solution, the new term arrives by the term $K_a$.

$p{K}_a=-log{K}_a$

$p{K}_a$ Values are used as measure of acidity; a strong acid will have a low $p{K}_a$ and a weak acid will have a high $p{K}_a$.

Using $p{K}_a$values to compare Basicity:  $p{K}_a$ Values are also used to compare bases; by drawing the conjugate acid of each base and compare the $p{K}_a$ values and identify the stronger base.