CuS (s) + 4 HNO₃ (aq) → Cu(NO₃)₂ (aq) + SO₂ (aq) + 2 NO (g) + 2 H₂O (l)

This is an oxidation-reduction (redox) reaction:

CuS is a reducing agent, HNO₃ is an oxidizing agent.

Reactants:

• CuS – Copper sulfide
  • Other names: Copper monosulfide , Covellite , Copper(II) sulfide , Cupric sulfide
  • Appearance: Black powder or lumps
• HNO₃ – Nitric acid
  • Other names: Aqua fortis , Spirit of niter , Eau forte ... show moreHydrogen nitrate , Acidum nitricum , Nitric acid (> 70% in water) , Fuming nitric acid , Engravers acid , HONO2 , Red fuming nitric acid , RFNA , White fuming nitric acid (WFNA) show less
  • 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.]

Products:

• Cu(NO₃)₂ – Copper(II) nitrate
  • Other names: Cupric nitrate , Nitrato de cobre (II) , Нитрат меди (II) (безводный) ... show moreНитрат меди(II) (anh.) , Cu (NO3)2 , Динитрат меди , Азотная кислота, соль меди(2+) , Нитрат меди , Нитрат меди(2+) show less
  • Appearance: Blue crystals | hygroscopic
• SO₂ – Sulfur dioxide
  • Other names: Sulfurous anhydride , Sulphur dioxide , Sulfurous acid anhydride ... show moreSulfurous oxide , Sulfur oxide , Sulphur dioxide , sulfur dioxide , SO2 , R-764 show less
  • Appearance: Colorless gas ; Colourless gas or compressed liquefied gas with pungent odour ; Colorless gas with a characteristic, irritating, pungent odor. [Note: A liquid below 14°F. Shipped as a liquefied compressed gas.]
• NO – Nitrogen monoxide , Oxidonitrogen(•) (additive)
  • Other names: Nitric oxide , Nitrogen(II) oxide , Nitric oxide (radical) ... show moreMononitrogen monoxide , (.)NO , EDRF , Nitrogen monooxide , [NO] , Oxido de nitrogeno(ii) , NO(.) , Oxido nitrico , Stickstoff(ii)-oxid , NO , Oxyde azotique , Oxyde nitrique , Stickstoffmonoxid , Nitrosyl , (NO)(.) , Monoxido de nitrogeno , Endothelium-derived relaxing factor , Nitroxide radical , Nitroxyl , Nitrosyl radical , Hydroxyamine , Nitrogen oxide , Nitrogen protoxide , Nitrosyl hydride , Nitric Oxide show less
  • Appearance: Colourless gas ; Colourless compressed gas ; Colorless gas. [Note: Shipped as a nonliquefied compressed gas.]
• H₂O – Water, oxidane
  • Other names: Water (H2O) , Hydrogen hydroxide (HH or HOH) , Hydrogen oxide ... show moreDihydrogen monoxide (DHMO) (systematic name) , Hydrogen monoxide , Dihydrogen oxide , Hydric acid , Hydrohydroxic acid , Hydroxic acid , Hydrol , Μ-oxido dihydrogen , Κ1-hydroxyl hydrogen(0) show less
  • Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas