# How does a copper piece added in nitric acid change after nitrogen dioxide starts appearing?

There's an experiment I have no way of performing but want to know its results. The instructions (in short) are:

Dip a piece of copper in a glass of concentrated nitric acid, $\ce{HNO3}$, using a pincette. When a brown gas starts forming, take out the piece of copper and rinse it with water. Right after that dip it into $\ce{HgNO3}$ solution. Leave it in there for some time and then take it out of the solution. Rinse it with water and wipe it with a napkin.

How does the piece of copper look?

What I've worked out is that the first part can be written as: $$\ce{Cu (s) + 4HNO3 (aq) -> Cu(NO3)2 (aq) + 2NO2 (g) + 2H2O(l)}$$ and that $\ce{NO2}$ is the brown gas.

What I'm not sure about is why exactly I'm dipping the copper piece into a solution of $\ce{HgNO3}$ following the above reaction. And why am I rinsing it with water before dipping it into the $\ce{HgNO3}$ solution?

• @student States of aggregation should not be subscripted, it is not wrong, but the recommendations (Sec. 2.1.) are different. – Martin - マーチン May 12 '16 at 5:30
• @Martin-マーチン Thank you, will bear it in mind. – user25546 May 14 '16 at 7:22