Question

do you know this.check how much knowledge you have by answering the question
​

Answer 1

Answer:

Copper is a reddish-brown metal, widely used in plumbing and electrical wiring; it is perhaps most familiar to people in the United States in the form of the penny.  (Although since 1983, pennies are actually made of zinc surrounded by a paper-thin copper foil to give them the traditional appearance of pennies.)  Copper is oxidized by concentrated nitric acid, HNO3, to produce Cu2+ ions; the nitric acid is reduced to nitrogen dioxide, a poisonous brown gas with an irritating odor:

Cu(s)  +  4HNO3(aq)  ——>  Cu(NO3)2(aq)  +  2NO2(g)  +  2H2O(l)

When the copper is first oxidized, the solution is very concentrated, and the Cu2+ product is initially coordinated to nitrate ions from the nitric acid, giving the solution first a green, and then a greenish-brownish color.  When the solution is diluted with water, water molecules displace the nitrate ions in the coordinate sites around the copper ions, causing the solution to change to a blue color.

In dilute nitric acid, the reaction produces nitric oxide, NO, instead:

3Cu(s)  +  8HNO3(aq)  ——>  3Cu(NO3)2(aq)  +  2NO(g)  +  4H2O(l)

 

In the following demonstration, a balled-up piece of thin copper wire is added to about 100 mL of concentrated nitric acid; once the copper is added the evolution of nitrogen dioxide occurs quickly.  Once all of the copper has reacted, the solution is diluted with distilled water, changing the solution from a dark brown to a pale blue color.

This demonstration can be done with copper in the form of shot, pellets, thicker wire, or bars, but is a great deal slower than with copper wire.