Redox Reactions and Oxidation States
The concept of oxidation state is used in several reactions as given below. These reaction can also be explained using the definitions of oxidation and reduction involving election transfer or the gain and loss of oxygen.
Reaction of Metals with Dilute Acids
Consider the reaction of zinc with dilute sulfuric acid:
The oxidation state of zinc increases from 0(in Zn) to +2 (in ZnSo4) and so zinc as oxidised. The oxidation state of hydrogen decreases from +1 (in H2 So4) to 0 (in H2) and so hydrogen is reduced.
Note that in this reaction, the sulfats ion does not change. Therefore, the oxidation numbers of solfur (+6) and oxygen (-2) in the ion do not change. The changes are more easily seen using the ionic equation:
Because zinc is oxidised, it acts as a reducing agent. Hydrogen ions in the dilute acid are reduced and therefore acts as an oxdising agent.
Halide Displacement Reactions
Chlorine reacts with potassium iodide solution as in the following ionic equation
On one hand, chlorine reduced-the oxidation number decreases. On the other hand,iodide iodide ions are oxidised-the oxidation number increases.