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Chapter 4: Problem 96

Gold metal will not dissolve in either concentrated nitric acid or concentrated hydrochloric acid. It will dissolve, however, in aqua regia, a mixture of the two concentrated acids. The products of the reaction are the AuCl, \(^{-}\) ion and gaseous NO. Write a balanced equation for the dissolution of gold in aqua regia.

Short Answer

Expert verified
The balanced chemical equation for the dissolution of gold in aqua regia is: \( Au (s) + 3 HNO_3 (aq) + 4 HCl (aq) \rightarrow AuCl_4^{-} (aq) + 3 NO (g) + 3 H_2O (l) \)

Step by step solution

01

Write the unbalanced equation

First, we will write the unbalanced equation representing the reaction of gold with aqua regia, which contains nitric acid and hydrochloric acid: Au (s) + HNO₃ (aq) + HCl (aq) → AuCl₄⁻ (aq) + NO (g) Next, we need to balance this equation.
02

Balance the gold atoms

There is already one gold atom on both sides of the equation, so it is already balanced with respect to gold: Au (s) + HNO₃ (aq) + HCl (aq) → AuCl₄⁻ (aq) + NO (g)
03

Balance the chlorine atoms

There are 4 chlorine atoms in AuCl₄⁻, so we need to put a coefficient of 4 in front of HCl to balance the chlorine atoms: Au (s) + HNO₃ (aq) + 4 HCl (aq) → AuCl₄⁻ (aq) + NO (g)
04

Balance the nitrogen atoms

There is one nitrogen atom in the reactant side (HNO₃) and one in the product side (NO), so the nitrogen atoms are already balanced: Au (s) + HNO₃ (aq) + 4 HCl (aq) → AuCl₄⁻ (aq) + NO (g)
05

Balance the hydrogen and oxygen atoms

From the reactants' side, we have one hydrogen atom from HNO₃ and four from the 4 HCl molecules, giving 5 hydrogen atoms in total. There are none in the products side, so we need to add water (H₂O) as a product to balance the H atoms. We add 3 H₂O molecules which contain a total of 6 H atoms and 3 O atoms. Also, to balance the O atoms, HNO₃ should be changed to 3 HNO₃ since it has 3 O atoms with 3 NO: Au (s) + 3 HNO₃ (aq) + 4 HCl (aq) → AuCl₄⁻ (aq) + 3 NO (g) + 3 H₂O (l) Now, we have a balanced chemical equation for the dissolution of gold in aqua regia: Au (s) + 3 HNO₃ (aq) + 4 HCl (aq) → AuCl₄⁻ (aq) + 3 NO (g) + 3 H₂O (l)

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Most popular questions from this chapter

The blood alcohol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) level can be determined by tirrating a sample of blood plasma with an acidic potassium dichromate solution, resulting in the production of \(\mathrm{Cr}^{3+}(a q)\) and carbon dioxide. The reaction can be monitored because the dichromate ion \(\left(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\right)\) is orange in solution, and the \(\mathrm{Cr}^{3+}\) ion is green. The unbalanced redox equation is $$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q) \rightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{CO}_{2}(g)$$ If 31.05 \(\mathrm{mL}\) of 0.0600\(M\) potassium dichromate solution is required to titrate 30.0 \(\mathrm{g}\) of blood plasma, determine the mass percent of alcohol in the blood.

Write net ionic equations for the reaction, if any, that occurs when aqueous solutions of the following are mixed. a. ammonium sulfate and barium nitrate b. lead(II) nitrate and sodium chloride c. sodium phosphate and potassium nitrate d. sodium bromide and rubidium chloride e. copper(II) chloride and sodium hydroxide

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A 100.0-mL aliquot of 0.200 M aqueous potassium hydroxide is mixed with 100.0 mL of 0.200 M aqueous magnesium nitrate. a. Write a balanced chemical equation for any reaction that occurs. b. What precipitate forms? c. What mass of precipitate is produced? d. Calculate the concentration of each ion remaining in solution after precipitation is complete.
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