Chemical Reaction: Copper and Nitric Acid

Which pair of substances would react the fastest?

a. Copper sheet and concentrated nitric acid.
b. Copper powder and dilute nitric acid.
c. Copper powder and concentrated nitric acid.

Answer:

c. Copper powder and concentrated nitric acid.

The pair of substances that would react the fastest between copper and nitric acid is copper powder and concentrated nitric acid. This is because the rate of a chemical reaction increases with both increased surface area of the solid reactant and the concentration of the acid. Copper powder has a high surface area which facilitates more reaction sites, and concentrated nitric acid provides a larger number of reactive molecules compared to a dilute solution.

The reaction of copper with concentrated nitric acid is also more vigorous than with dilute acid. When concentrated nitric acid reacts with copper, it typically produces copper (II) nitrate and nitrogen dioxide along with water. The blue color of the solution is indicative of the copper ions, and the evolution of brown fumes is due to nitrogen dioxide. Moreover, a fine powder will react more quickly than a solid sheet due to the increased surface area interacting with the acid.