CuS + 8 HNO₂ → Cu(NO₃)₂ + S + 6 NO + 4 H₂O

This is an oxidation-reduction (redox) reaction:

CuS is a reducing agent, HNO₂ is an oxidizing agent, HNO₂ is a reducing agent.

Reactants:

• CuS – Copper sulfide
  • Other names: Copper monosulfide , Covellite , Copper(II) sulfide , Cupric sulfide
  • Appearance: Black powder or lumps
• HNO₂ – Nitrous acid , Hydroxidooxidonitrogen
  • Other names: HNO2 , [NO(OH)] , Nitrosyl hydroxide , Dioxonitric acid
  • Appearance: Pale blue solution

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
• S
  • Names: Sulfur , S , Sulphur ... show moreElement 16 , Flowers of sulfur , Flour sulfur , Brimstone show less
  • Appearance: Yellow solid in various forms
• 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