Chemistry > Balancing Reaction > 2.0 Balancing redox reactions
Balancing Reaction
1.0 Balancing chemical equations
2.0 Balancing redox reactions
2.2 Oxidising and reducing agents
Oxidising agent
Oxidising agent, or oxidant, gains electrons and is reduced in a chemical reaction.
Also known as the electron acceptor, the oxidising agent is normally in one of its higher possible oxidation states because it will gain electrons and be reduced.
Reducing agent
A reducing agent, or reductant, loses electrons and is oxidized in a chemical reaction.
A reducing agent is typically in one of its lower possible oxidation states, and is known as the electron donor.
A reducing agent is oxidised, because it loses electrons in the redox reaction.
The functioning of some common oxidising and reducing agent is summarised below,
| Oxidising agent | Effective change | Decrease in oxidation number per atom |
| $KMnO_4$ in acid solution | $MnO_4^ - \to M{n^{ + 2}}$ | 5 |
| $KMnO_4$ in alkaline solution | $MnO_4^ - \to Mn{O_2}$ | 3 |
| $K_2Cr_2O_7$ in acid solution | $C{r_2}O_7^{2 - } \to C{r^{ + 3}}$ | 3 |
| Dilute $HNO_3$ | $NO_3^ - \to NO$ | 3 |
| Concentrated $HNO_3$ | $NO_3^ - \to N{O_2}$ | 1 |
| Concentrated $H_2SO_4$ | $SO_4^{2 - } \to S{O_2}$ | 2 |
| Manganese (IV) oxide | $Mn{O_2} \to M{n^{ + 2}}$ | 2 |
| Chlorine | $C{l_2} \to C{l^ - }$ | 1 |
| Chloric (I) acid | $Cl{O^ - } \to C{l^ - }$ | 2 |
| $KIO_3$ in dilute acid | $IO_3^ - \to {I_2}$ | 5 |
| $KIO_3$ in concentrated acid | $IO_3^ - \to {I^ - }$ | 6 |
| Oxidising agent | Effective change | Decrease in oxidation number per atom |
| Iron (II) salts (acid) | $F{e^{ + 2}} \to F{e^{ + 3}}$ | 1 |
| Tin (II) salts (acid) | $S{n^{ + 2}} \to S{n^{ + 4}}$ | 2 |
| Ethanedioates (acid) | ${C_2}O_4^{2 - } \to C{O_2}$ | 1 |
| Sulphites (acid) | $SO_3^{2 - } \to SO_4^{2 - }$ | 2 |
| Hydrogen sulphide | ${S^{2 - }} \to S$ | 2 |
| Iodides (dilute acid) | ${I^ - } \to I$ | 1 |
| Iodides (concentrated acid) | ${I^ - } \to {I^ + }$ | 2 |
| Metals e.g. Zinc | $Zn \to Z{n^{ + 2}}$ | 2 |
| Hydrogen | $H \to {H^ + }$ | 1 |
