HClO4 + 4 H2SO3 → HCl + 4 H2SO4

This is an oxidation-reduction (redox) reaction:

4 SIV - 8 e- → 4 SVI (oxidation)

ClVII + 8 e- → Cl-I (reduction)

H2SO3 is a reducing agent, HClO4 is an oxidizing agent.

Reactants:

  • HClO4 – Chloric(VII) acid source: wikipedia, accessed: 2019-09-27
    • Other names: Perchloric acid source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02, Hyperchloric acid source: wikipedia, accessed: 2019-09-27, Perchloric acid (72% solution) source: ICSC, accessed: 2019-09-04, Hydronium perchlorate source: ICSC, accessed: 2019-09-04
    • Appearance: Colorless liquid source: wikipedia, accessed: 2019-09-27; Colourless liquid with pungent odour source: ICSC, accessed: 2019-09-04
  • H2SO3 – Sulfurous acid source: wikipedia, accessed: 2019-09-28source: wikidata, accessed: 2019-09-02
    • Other names: S(O)(OH)2 source: wikidata, accessed: 2019-09-02, Sulphurous acid source: wikidata, accessed: 2019-09-02

Products:

  • HCl – Chlorane source: wikipedia, accessed: 2019-09-27, Hydrogen chloride source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02
    • Other names: Hydrochloric acid source: wikipedia, accessed: 2019-09-27source: NIOSH NPG, accessed: 2019-09-02, M source: wikipedia, accessed: 2019-09-27, Uriatic acid source: wikipedia, accessed: 2019-09-27
    • Appearance: Colorless, transparent liquid, fumes in air if concentrated source: wikipedia, accessed: 2019-09-27; Colorless gas source: wikipedia, accessed: 2019-09-27; Colourless compressed liquefied gas with pungent odour source: ICSC, accessed: 2019-09-04; Colorless to slightly yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.] source: NIOSH NPG, accessed: 2019-09-02
  • H2SO4 – Sulfuric acid source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-07source: NIOSH NPG, accessed: 2019-09-02
    • Other names: Oil of vitriol source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-07source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02, Sulfuric acid, concentrated (> 51% and < 100%) source: ICSC, accessed: 2019-09-04, H2SO4 source: wikidata, accessed: 2019-09-07
    • Appearance: Clear, colorless liquid source: wikipedia, accessed: 2019-09-27; Odourless colourless oily hygroscopic liquid source: ICSC, accessed: 2019-09-04; Colorless to dark-brown, oily, odorless liquid. [Note: Pure compound is a solid below 51°F. Often used in an aqueous solution.] source: NIOSH NPG, accessed: 2019-09-02