Understanding Metal Reactions with Cold Dilute Nitric Acid and Hydrogen Evolution

In the context of chemical reactions, the interaction between metals and nitric acid (HNO3) is a fascinating phenomenon that varies widely depending on the type of metal and the concentration of the nitric acid solution. One critical distinction is the behavior of certain metals that can react with cold dilute nitric acid to produce hydrogen gas. This article explores which metals can evolve hydrogen when reacting with cold dilute nitric acid and the underlying chemistry behind these reactions.

Which Metals Evolve Hydrogen on Reacting with Cold Dilute HNO3

The metal that can evolve hydrogen when reacting with cold dilute nitric acid (HNO3) is zinc (Zn). Unlike other metals that react with dilute HNO3 to produce nitrogen oxides, zinc can displace hydrogen from the acid, leading to the evolution of hydrogen gas.

Here are some other notable metals that can react with cold dilute HNO3 to produce hydrogen gas:

Magnesium and Manganese Reactions with Cold Dilute HNO3

Magnesium (Mg) and manganese (Mn) both react with cold dilute nitric acid to produce hydrogen gas. However, it is crucial that the HNO3 be highly dilute with a concentration of 0.01M to prevent the oxidation of hydrogen to water. The chemical equation for the reaction between magnesium and cold dilute HNO3 is as follows:

Reaction:

Mg 2HNO3(0.01M) → Mg(NO3)2 H2

A similar reaction occurs with manganese:

Reaction:

Mn 2HNO3(0.01M) → Mn(NO3)2 H2

Nitric Acid as an Oxidizing Agent

Nitric acid is known for its strong oxidizing properties. It reduces hydrogen (H2) to water (H2O) and typically does not produce hydrogen gas. The only metals that can react with cold dilute nitric acid to produce hydrogen are magnesium (Mg) and calcium (Ca). Here is the reaction for magnesium:

Reaction:

Mg 2HNO3(aient) → Mg(NO3)2 H2

Factors Affecting Metal Reactions with Nitric Acid

The reaction of metals with nitric acid can vary significantly based on the concentration and form of the acid. For example, aluminum (Al) generally does not react much with dilute nitric acid because it quickly forms an oxide layer that protects the metal. However, in very dilute solutions, aluminum can react:

Reaction at low concentrations:

2Al 10HNO3(dilute) → 2Al(NO3)3 N2O↑ 5H2O

Reaction with more concentrated acid:

3Fe 6HNO3(dilute) → 3Fe(NO3)2 2NO↑ 3H2O

Similarly, copper (Cu) can also be used:

Reaction:

3Cu 8HNO3(dilute) → 3Cu(NO3)2 2NO↑ 4H2O

These reactions occur due to the strong oxidizing nature of nitric acid, which prevents the production of hydrogen. The tendency of a metal to react with nitric acid is determined by the reduction potentials of the involved species.

Conclusion

While nitric acid is a powerful oxidizing agent, only a select few metals can react with cold dilute nitric acid to produce hydrogen gas. Specific conditions, such as the concentration and form of the nitric acid, play a crucial role in these reactions. Understanding the underlying electrochemical principles helps explain these unique behaviors in metal-nitric acid interactions. This knowledge is invaluable for chemists and industrial applications where controlled reactions are essential.