Chlorine Dioxide
Definition and meaning of Chlorine Dioxide in chemistry.
Chlorine dioxide is a small, reddish-yellow gaseous compound of chlorine and oxygen (ClO2) that acts as a powerful, selective oxidizing agent. It is best known as a disinfectant for drinking water and wastewater and as a bleaching agent for wood pulp.
In more detail
The molecule has a bent shape with an odd number of valence electrons, making it a stable free radical (chlorine in the +4 oxidation state). This radical character drives its strong oxidizing power, allowing it to inactivate bacteria, viruses, and protozoa (including Giardia and Cryptosporidium) without producing the high levels of chlorinated organic byproducts, such as trihalomethanes, associated with chlorine gas disinfection. Because pure ClO2 is unstable, explosive under pressure or light, and cannot be shipped as a compressed gas, it is always generated on-site, typically by reacting sodium chlorite with chlorine gas or an acid.
Key facts
| Formula | ClO2 |
|---|---|
| Field | Inorganic Chemistry |
| Molar mass | 67.45 g/mol |
| Chlorine oxidation state | +4 |
A municipal water treatment plant generates chlorine dioxide on-site by combining sodium chlorite (NaClO2) with chlorine gas, then injects the dilute ClO2 solution into the water stream to disinfect it while minimizing trihalomethane formation.
Frequently asked questions
Is chlorine dioxide the same as chlorine gas?
No. Chlorine gas (Cl2) has chlorine in the 0 oxidation state and forms chlorinated organic byproducts more readily, while ClO2 has chlorine in the +4 state, is a distinct radical molecule, and produces different, generally fewer, disinfection byproducts.
Why isn't chlorine dioxide transported as a compressed gas?
Concentrated ClO2 gas is thermally and photochemically unstable and can decompose explosively into chlorine and oxygen, so it is generated on-site at low concentration immediately before use.