1. The problem statement, all variables and given/known data Difference between nitric acid added to the mixture Copper Oxide + Carbon and nitric acid added to the mixture Copper + Carbon Dioxide 2. Relevant equations meteal oxide + carbon ---> metal + carbon dioxide 3. The attempt at a solution When I added Nitric Acid to the mixture Copper Oxide + Carbon no reaction had occured, when i then added it to copper + Carbon Dioxide (after a reducation reaction) a brown gas had formed, is the reason behind the formation of brown gas due to nitric acid reacting with copper? Or am i completely wrong.