2 Na2S2O3 + I2 → Na2S4O6 + 2 NaI

This is an oxidation-reduction (redox) reaction:

4 SII - 2 e- → 4 S5/2 (oxidation)

2 I0 + 2 e- → 2 I-I (reduction)

Na2S2O3 is a reducing agent, I2 is an oxidizing agent.

Reactants:

  • Na2S2O3
    • Names: Sodium thiosulfate source: wikipedia, accessed: 2019-09-28source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Sodium hyposulfite source: wikipedia, accessed: 2019-09-28source: wikidata, accessed: 2019-09-02, Hyposulphite of soda source: wikipedia, accessed: 2019-09-28
    • Appearance: White crystals source: wikipedia, accessed: 2019-09-28; Colourless 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

Products:

  • Na2S4O6
    • Names: Sodium tetrathionate source: wikidata, accessed: 2019-09-03
  • NaI
    • Names: Sodium iodide source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02, Sodium iodide (anhydrous) source: ICSC, accessed: 2019-09-04, NaI source: wikidata, accessed: 2019-09-02, Sodium monoiodide source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04
    • Appearance: White solid | deliquescent source: wikipedia, accessed: 2019-09-27; Colourless-to-white hygroscopic crystals or white powder. turns brown on exposure to air source: ICSC, accessed: 2019-09-04