Question

[CoCl₄]²⁻ (blue) + 6H₂O ⇌ [Co(H₂O)₆]²⁺ (pink) + 4Cl⁻

Determine the oxidation state for each element in the reaction above. Is this an example of an oxidation-reduction reaction?

Answer 1

The oxidation state for Co is +2, for Cl is -1, for O is -2, and for H is +1 in both the reactants and products, indicating no change in oxidation states and confirming that the reaction is not a redox reaction but a reversible reaction.

Step-by-step explanation:

The reaction you've asked about is:

[CoCl4]2- (blue) + 6H2O ⇌ [Co(H2O)6]2+ (pink) + 4Cl-

Let's determine the oxidation states for each element in the reaction:

• For Co in [CoCl4]2- and [Co(H2O)6]2+, the oxidation state is +2 because the overall charge on the complexes are due to the cobalt ion.
• Cl in [CoCl4]2- and as Cl- has an oxidation state of -1.
• Oxygen in the H2O molecule has an oxidation state of -2, following the rule that oxygen is generally -2 except in peroxides.
• Hydrogen from H2O molecules has an oxidation state of +1.

This reaction is not an example of an oxidation-reduction (redox) reaction because there is no change in oxidation states of elements throughout the reaction. The cobalt and chlorine maintain their oxidation states before and after the reaction. This is instead an example of a reversible reaction, also known as a chemical equilibrium, where the formation of a complex ion occurs.