Question

What are some examples of reduction reactions?

Answer 1

Reduction can be considered as the removal of oxygen, the addition of hydrogen, or the gain of electrons.

Removal of oxygen:
Metal ores which are oxides are reduced to the metal - this is how iron is made from iron ore. The reducing agent is carbon monoxide.
`Fe_2O_3` + `3CO` --> `2Fe` + `3CO_2`

Addition of hydrogen:
Aldehydes and ketones can be reduced to primary or secondary alcohols respectively using aqueous sodium borohydride. This is a source of `H^-` ions which bring about the reduction:
`CH_3CHO` + `2[H]` --> `CH_3CH_2OH`

Copper oxide can be reduced to copper by heating it while passing hydrogen gas over it. The hydrogen gets oxidised to form water.
`CuO` + `H_2` --> `Cu` + `H_2O`

Gain of electrons:
The formation of non-metal ions from the corresponding element, for example during electrolysis, is an example of this, e.g.
`Cl_2` + `2e^-` --> `2Cl^-`

In the same way, positive metal ions can gain electrons to be reduced to the metallic element:
`Cu^(2+)` + `2e^-` --> `Cu`