Relative oxidising/reducing strengths

The oxidants and reductants that we have already studied have different oxidising and reducing strengths.

The electrochemical series shown in the table below lists redox couples (oxidant/reductant pairs) in order of reduction potential or E^o value.

A redox couple consists of an oxidant (on the left) and its conjugate reductant (on the right).

The reduction potential measures how easily the oxidant atom or ion can be reduced, and electrons added to it.

A high positive E^o value means that the oxidant atom/ion is very easy to reduce (but the reverse reaction - the oxidation of the reductant - will be very difficult.

A high negative E^o value means that the oxidant atom/ion is very difficult to reduce (but the reverse reaction - the oxidation of the reductant - will be very easy.

An oxidant will oxidise the reductant of any redox couple which has a lower (more negative) reduction potential.

Fluorine, F₂ is the strongest oxidant as it has the most positive E^o value.

Fluoride ions, F^- the weakest reductant as it has the most positive E^o value.

Lithium, Li is the strongest reductant as it has the most negative E^o value.

Lithium ions, Li⁺ is the weakest oxidant as it has the most negative E^o value.