Chapter 19, Problem 19.97QP

(a)

Interpretation Introduction

Interpretation:

The complete balanced equation for the dissolution of gold in aqua regia has to be found and the purpose of the addition of hydrochloric acid to the reaction mixture should be explained.

Concept Introduction:

Dissolution of gold in aqua regia: Aqua regia is the mixture of ${\text{HNO}}_{\text{3}}$ and $\text{HCl}$ in the ratio of $\text{1:3}$.  Neither of the acids can dissolve gold individually.  But the aqua regia can dissolve gold and platinum.  Nitric acid being a power full oxidising agent oxidises a very small amount of $\text{Au}$ to ${\text{Au}}^{+3}$.  The formed gold ions later reacts with the chloride ions produced by the $\text{HCl}$ and forms ${\text{AuCl}}_4{}^{-}$.  The excess of hydrogen ions present in the solution stabilises the complex ion and also leads to the formation of chloroauric acid ${\text{(HAuCl}}_4)$.

A chemical equation is the figurative representation of chemical reaction.  In a chemical equation the reactants are in the left side and the products are in the right side.  A balanced chemical equation serves as an easy tool for understanding a chemical reaction.

(b)

Interpretation Introduction

Interpretation:

The complete balanced equation for the dissolution of gold in aqua regia has to be found and the purpose of the addition of hydrochloric acid to the reaction mixture should be explained.

Concept Introduction:

Dissolution of gold in aqua regia: Aqua regia is the mixture of ${\text{HNO}}_{\text{3}}$ and $\text{HCl}$ in the ratio of $\text{1:3}$.  Neither of the acids can dissolve gold individually.  But the aqua regia can dissolve gold and platinum.  Nitric acid being a power full oxidising agent oxidises a very small amount of $\text{Au}$ to ${\text{Au}}^{+3}$.  The formed gold ions later reacts with the chloride ions produced by the $\text{HCl}$ and forms ${\text{AuCl}}_4{}^{-}$.  The excess of hydrogen ions present in the solution stabilises the complex ion and also leads to the formation of chloroauric acid ${\text{(HAuCl}}_4)$.

A chemical equation is the figurative representation of chemical reaction.  In a chemical equation the reactants are in the left side and the products are in the right side.  A balanced chemical equation serves as an easy tool for understanding a chemical reaction.