2 KIO3 (aq) + 5 SO2 (aq) + 4 H2O (l) → K2SO4 (aq) + I2 (s) + 4 H2SO4 (aq)

This is an oxidation-reduction (redox) reaction:

5 SIV - 10 e- → 5 SVI (oxidation)

2 IV + 10 e- → 2 I0 (reduction)

SO2 is a reducing agent, KIO3 is an oxidizing agent.

Reactants:

  • KIO3 – Potassium iodate source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02
    • Other names: Iodic acid source: wikipedia, accessed: 2019-09-27, Potassium salt source: wikipedia, accessed: 2019-09-27, KIO3 source: wikidata, accessed: 2019-09-02
    • Appearance: White crystalline powder source: wikipedia, accessed: 2019-09-27
  • SO2 – Sulfur dioxide source: wikipedia, accessed: 2019-09-28source: wikidata, accessed: 2019-09-02source: NIOSH NPG, accessed: 2019-09-02
    • Other names: Sulfurous anhydride source: wikipedia, accessed: 2019-09-28source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Sulphur dioxide source: ICSC, accessed: 2019-09-04source: wikidata, accessed: 2019-09-02, Sulfurous acid anhydride source: wikidata, accessed: 2019-09-02source: NIOSH NPG, accessed: 2019-09-02
    • Appearance: Colorless gas source: wikipedia, accessed: 2019-09-28; Colourless gas or compressed liquefied gas with pungent odour source: ICSC, accessed: 2019-09-04; Colorless gas with a characteristic, irritating, pungent odor. [Note: A liquid below 14°F. Shipped as a liquefied compressed gas.] source: NIOSH NPG, accessed: 2019-09-02
  • H2O – Water, oxidane source: wikipedia, accessed: 2019-09-27
    • Other names: Water (H2O) source: wikipedia, accessed: 2019-09-27, Hydrogen hydroxide (HH or HOH) source: wikipedia, accessed: 2019-09-27, Hydrogen oxide source: wikipedia, accessed: 2019-09-27
    • Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas source: wikipedia, accessed: 2019-09-27

Products:

  • K2SO4
    • Names: Potassium sulfate source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Potassium sulphate source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02, Dipotassium sulfate source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04
    • Appearance: White solid source: wikipedia, accessed: 2019-09-27; Colourless-to-white crystals source: ICSC, accessed: 2019-09-04
  • I2
    • Names: Iodine source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02, Jod source: ICSC, accessed: 2019-09-04, Iode source: ICSC, accessed: 2019-09-04
    • Appearance: Bluish black or dark purple crystals with pungent odour source: ICSC, accessed: 2019-09-04; Violet solid with a sharp, characteristic odor. 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