Question

Complete and balance the following reaction:

${\mathrm{HNO}}_3+\mathrm{HCl}\left(\mathrm{conc}\right)\to$

Answer 1

• When Hydrochloric acid ($\mathbf{HCl}$) reacts with Nitric Acid (${\mathbf{HNO}}_{\mathbf{3}}$) it forms Nitrosyl chloride ($\mathbf{NOCl}$), water, and Nascent chlorine.
• A mixture of Nitric acid and Hydrochloric acid, at a molar ratio of 1:3 optimally is also known as Aqua regia.
• Aqua regia can dissolve noble metals such as gold and platinum.
• The chemical reaction is as follows:

$\underset{(\mathrm{Nitric}\mathrm{acid})}{{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Nitrosyl}\mathrm{chloride})}{\mathrm{NOCl}\left(\mathrm{g}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

Step 1: Balancing the reaction:

• In order to balance such equation we first calculate the number of molecules on both sides of the reaction.
• On the reactant side: 1 Hydrogen, 1 Nitrogen, and 3 Oxygen are present in Nitric acid
• Similarly, 1 Hydrogen and 1 Chlorine are present in Hydrogen chloride.
• On the product side: 1 Nitrogen, 1 Oxygen, and 1 Chlorine are present in Nitrosyl chloride.
• Similarly, 2 Hydrogen and 1 Oxygen are present in the water molecule and 2 Chlorine molecules are also liberated.

Step 2: Balancing the reactant molecules: Multiplying 3 with Hydrogen chloride.

• The chemical equation is as follows: $\underset{(\mathrm{Nitric}\mathrm{acid})}{{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{3\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Nitrosyl}\mathrm{chloride})}{\mathrm{NOCl}\left(\mathrm{g}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$
• The number of molecules of Hydrogen is more on the reactants side, therefore we have to balance the product side as well.

Step 3: Balancing the product molecules: Multiplying 2 with a water molecule.

• The chemical equation is as follows: $\underset{(\mathrm{Nitric}\mathrm{acid})}{{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{3\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Nitrosyl}\mathrm{chloride})}{\mathrm{NOCl}\left(\mathrm{g}\right)}+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$
• Thus, we balance both sides of the equation i.e. a number of reactant molecules are equal to the product molecules.
• On the reactant side: 1 Hydrogen, 1 Nitrogen, and 3 Oxygen are present in Nitric acid
• Similarly, 3 Hydrogen and 3 Chlorine are present in Hydrogen chloride.
• On the product side: 1 Nitrogen, 1 Oxygen, and 1 Chlorine are present in Nitrosyl chloride.
• Similarly, 4 Hydrogen and 2 Oxygen are present in the water molecule and 2 Chlorine molecules are also liberated.

Thus, the complete balance equation is as follows:$\underset{(\mathrm{Nitric}\mathrm{acid})}{{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{3\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Nitrosyl}\mathrm{chloride})}{\mathrm{NOCl}\left(\mathrm{g}\right)}+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+2{\mathrm{Cl}}_2\left(\mathrm{g}\right)$