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Copper is an unreactive metal and doesn’t react in normal circumstances with dilute acids. However it does react with nitric acid. Which of the following equations represent how Copper reacts with DILUTE nitric acid?

$\begin{array}{1 1}(A) 3Cu + 8HNO_3 \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O \\ (B) Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2NO + 2H_2O \\ (C) 3Cu + 8HNO_3 \rightarrow Cu(NO_3)_4 + NO + 2H_2O \\ (D) Cu + 4HNO_3 \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O \end{array} $

1 Answer

There are two equations for the reaction of copper with nitric acid. It depends on whether the nitric acid is concentrated or not.
If it is concentrated and in excess then the ratio is 1:4 copper to nitric acid. If it is dilute then the ratio is 3:8.
For example, copper reacts with DILUTE nitric acid at ambient temperatures with a 3:8 stoichiometry.
$(A) 3Cu + 8HNO_3 –> 3Cu(NO_3)_2 + 2NO + 4H_2O$ which is the answer
$(B) Cu + 4HNO_3 –> Cu(NO_3)_2 + 2NO + 2H_2O$ is the reaction with CONCENTRATED Nitric acid.
answered Mar 16, 2014 by balaji.thirumalai