CuS (s) + 10 HNO3 (aq) → Cu(NO3)2 (aq) + H2SO4 (aq) + 8 NO2 (l) + 4 H2O (l)
This is an oxidation-reduction (redox) reaction:
S-II - 8 e- → SVI (oxidation)
8 NV + 8 e- → 8 NIV (reduction)
CuS is a reducing agent, HNO3 is an oxidizing agent.
Reactants:
- CuS – Copper sulfide

- HNO3 – Nitric acid



- Other names: Aqua fortis


, Spirit of niter 
, Eau forte 
- Appearance: Colorless, yellow or red fuming liquid
; Colourless-to-yellow liquid with pungent odour
; Colorless, yellow, or red, fuming liquid with an acrid, suffocating odor. [Note: Often used in an aqueous solution. Fuming nitric acid is concentrated nitric acid that contains dissolved nitrogen dioxide.] 
- Other names: Aqua fortis
Products:
- Cu(NO3)2 – Copper(II) nitrate


- H2SO4 – Sulfuric acid



- NO2 – Nitrogen dioxide




- Other names: Nitrogen(IV) oxide
, Deutoxide of nitrogen
, Nitrogen peroxide 


- Appearance: Brown gas
; Reddish-brown gas or brown or yellow liquid with pungent odour
; Yellowish-brown liquid or reddish-brown gas (above 70°F) with a pungent, acrid odor. [Note: In solid form (below 15°F) it is found structurally as N2O4.] 
- Other names: Nitrogen(IV) oxide
- H2O – Water, oxidane
