Chapter 18, Problem 18.25P

(a)

Interpretation Introduction

Interpretation:

The value of $\text{Kc > 1}$ for the given ${\text{OH}}^{-}{\text{ + HS}}^{-}\underset{}{\rightleftharpoons }{\text{ H}}_2^{}{\text{O + S}}_{}^{2-}$ acid - base reaction has to be determined.

Concept introduction:

Conjugate acid-Base pairs:

The acid donates the proton to form its conjugate base and the base accepts a proton to form its conjugate acid.

When an acid is dissolved in water, the acid $\text{(HA)}$ donates a proton to water to form a new acid (conjugate acid) and a new base (conjugate base).

The pair of an Acid –Base differs by a proton called conjugated Acid-Base pair.

In acid – base reaction, if the stronger acid produces the weaker acid which tells that the reaction favors the products, and the $\text{Kc}$ value is greater than one $\left(\text{Kc > 1}\right)$. If the weaker acid produces the stronger acid which tells that the reaction favors the reactants, and the $\text{Kc}$ value is less than one $\left(\text{Kc < 1}\right)$.

(b)

Interpretation Introduction

Interpretation:

The value of $\text{Kc > 1}$ for the given ${\text{HCN + HCO}}_{\text{3}}^{\text{-}}\underset{}{\rightleftharpoons }{\text{ H}}_{\text{2}}^{}{\text{CO}}_{\text{3}}{\text{ + CN}}_{}^{\text{-}}$ acid - base reaction has to be determined.

Concept introduction:

Conjugate acid-Base pairs:

The acid donates the proton to form its conjugate base and the base accepts a proton to form its conjugate acid.

When an acid is dissolved in water, the acid $\text{(HA)}$ donates a proton to water to form a new acid (conjugate acid) and a new base (conjugate base).

The pair of an Acid –Base differs by a proton called conjugated Acid-Base pair.

In acid – base reaction, if the stronger acid produces the weaker acid which tells that the reaction favors the products, and the $\text{Kc}$ value is greater than one $\left(\text{Kc > 1}\right)$. If the weaker acid produces the stronger acid which tells that the reaction favors the reactants, and the $\text{Kc}$ value is less than one $\left(\text{Kc < 1}\right)$.