How to prove that there is nitric acid in a test tube? Write an equation and a sign.

A qualitative reaction to nitric acid is its reaction with metallic copper. A piece of purified metallic copper is placed in a test tube containing nitric acid, a reaction takes place, gas is released. At the same time, brown gas is released, which has a name – “fox’s tail”, the gas is very dangerous, therefore the experiment is carried out under an exhaust hood. Often the gas is brown in color, can be seen near the hoods of large factories, this is due to the fact that the factories use nitric acid. This reaction looks like this: 2HNO3 + Cu = Cu (OH) 2 + 2NO2.