Thu August 16, 2012 By: Ashwin Srinath

sulphur dioxide is a reducing agent but tellurium dioxide is an oxidising agent,why?

Expert Reply
Fri August 17, 2012
Oxidation no. of sulphur changes from 0 to +4 in SO2. Due to presence of d-orbitals(vacant) sulphur can extend its covalency & show oxidation states till +6, which is stable in sulphur (eg: SF6).

Hence it acts as a reducing agent. (PS it acts as both oxidising and reducing agent)

Oxidation no. of Te changes from 0 to +4 in TeO2. Unlike sulphur Te cannot show +6 oxidation state as it is highly unstable due to inert pair effect. Therefore there can only be a decrease in it oxidation state (it can decrease to -2, +2). Also, TeO2 is a polymeric oxide which is not very much stable.

Hence it acts as an oxidising agent.

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