3 S (s) + 4 HNO3 (aq) → 4 NO (g) + 3 SO2 (aq) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
3 S0 - 12 e- → 3 SIV (oxidation)
4 NV + 12 e- → 4 NII (reduction)
S is a reducing agent, HNO3 is an oxidizing agent.
Reactants:
- S
- 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.]
Products:
- NO – Nitrogen monoxide , Oxidonitrogen(•) (additive)
- SO2 – Sulfur dioxide
- Other names: Sulfurous anhydride , Sulphur dioxide , Sulfurous acid anhydride
- 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.]
- H2O – Water, oxidane