Obtaining a Higher Concentration of Nitric Acid via Combination with Concentrated Sulfuric Acid and Redistillation

Nitric acid (HNO3) is a key reagent in many industrial and analytical processes. However, achieving higher concentrations of nitric acid can be challenging due to its tendency to form an azeotrope with water. This article explores how combining nitric acid with concentrated sulfuric acid (H2SO4) and redistilling the mixture can achieve higher concentrations of nitric acid.

Dehydrating Agent

Concentrated sulfuric acid acts as a strong dehydrating agent, playing a crucial role in the process. When mixed with nitric acid, sulfuric acid removes the water produced during the reaction, driving the equilibrium toward the formation of more nitric acid. This process can be represented by the following simplified reaction:

[text{HNO}_3 text{H}_2text{SO}_4 rightarrow text{HSO}_3text{NO}_2 text{H}_2text{O}]

In this reaction, sulfuric acid absorbs the water that is produced, shifting the reaction equilibrium to favor the formation of nitric acid. This enhances the concentration of nitric acid in the mixture.

Azeotrope Formation

When nitric acid is distilled alone, it forms an azeotrope with water, which limits the achievable concentration. An azeotrope is a constant boiling point mixture. By using sulfuric acid in the distillation process, the presence of sulfuric acid alters the distillation conditions. This allows for the separation of nitric acid from water more effectively, leading to a higher concentration of nitric acid.

Higher Boiling Point

The addition of sulfuric acid raises the boiling point of the mixture. During the redistillation process, this higher boiling point can facilitate better separation of nitric acid from water. More volatile components, including water, are distilled off, leaving behind a more concentrated solution of nitric acid.

Concentration Process

The distillation process itself is essential for concentrating the nitric acid. As the mixture is heated, components vaporize. The more volatile nitric acid can be collected separately, while the concentrated sulfuric acid remains in the distillation flask. This further facilitates the concentration of nitric acid in the distillate.

In summary, the combination of sulfuric acid's dehydrating properties, the alteration of boiling points, and the ability to effectively separate nitric acid from water during distillation results in obtaining a higher concentration of nitric acid. This process is pivotal in various industrial applications, ensuring the efficient production and use of nitric acid.

Keywords: nitric acid, concentrated sulfuric acid, redistillation, azeotrope, dehydrating agent