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Chapter 18: Problem 101

Gold will not dissolve in either concentrated nitric acid or concentrated hydrochloric acid. However, the metal does dissolve in a mixture of the acids (one part \(\mathrm{HNO}_{3}\) and three parts \(\mathrm{HCl}\) by volume \()\) called aqua regia. (a) Write a balanced equation for this reaction. (Hint: Among the products are \(\mathrm{HAuCl}_{4}\) and \(\mathrm{NO}_{2} .\) ) (b) What is the function of \(\mathrm{HCl} ?\)

Short Answer

Expert verified
The balanced chemical equation for this reaction is \(\mathrm{Au + 4 HNO}_{3} + \mathrm{4 HCl} \rightarrow \mathrm{HAuCl}_{4} + \mathrm{4 NO}_{2} + 2 \mathrm{H}_{2}O\). The function of \(\mathrm{HCl}\) in this reaction is to provide chloride (\(\mathrm{Cl}^{-}\)) ions, which are necessary for the formation of the \(\mathrm{HAuCl}_{4}\) complex when gold dissolves.

Step by step solution

01

Write the unbalanced chemical equation

Given that gold (Au) reacts with nitric acid (\(\mathrm{HNO}_{3}\)) and hydrochloric acid (\(\mathrm{HCl}\)) to produce tetrachloroaurate (\(\mathrm{HAuCl}_{4}\)) and nitrogen dioxide (\(\mathrm{NO}_{2}\)), the first step is to write the unbalanced equation. Thus, the equation is: \(\mathrm{Au + HNO}_{3} + \mathrm{HCl} \rightarrow \mathrm{HAuCl}_{4} + \mathrm{NO}_{2}\)
02

Balance the chemical equation

Next step is to balance this equation. Balancing chemical equations involving several atoms can be complicated, so make sure you have the correct amount of atoms on each side. The balanced equation is: \(\mathrm{Au + 4 HNO}_{3} + \mathrm{4 HCl} \rightarrow \mathrm{HAuCl}_{4} + \mathrm{4 NO}_{2} + 2 \mathrm{H}_{2}O\)
03

Explain the role of HCl

The last step is to explain the function of hydrochloric acid (\(\mathrm{HCl}\)). In this reaction, \(\mathrm{HCl}\) acts as a source of chloride (\(\mathrm{Cl}^{-}\)) ions. These chloride ions are required to form the \(\mathrm{HAuCl}_{4}\) complex when gold (Au) dissolves.

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Most popular questions from this chapter

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