2.7 Hydrogen peroxide

2.7 Hydrogen peroxide

Disproportionation

Disproportionation is when a species can either be oxidised or reduced. Hydrogen peroxide (H₂O₂) is a good example of this.

Hydrogen Peroxide Oxidation

H₂O_2(aq)    -->   O_2(g)  + 2H⁺_(aq) + 2e                 (oxidation)

The oxygen in H₂O₂ has an oxidation number of -1 this is increased to 0 in O₂. Therefore this is oxidation.

Hydrogen Peroxide Reduction

H₂O_{2 (aq)}     +  2H⁺_(aq)    + 2e^-   -->    2H₂O_(l) (reduction) 

The oxygen in H₂O₂ has an oxidation number of -1 this is decreased to -2 in H₂O. Therefore this is reduction.

Is it oxidation or reduction???

You have to look at what the hydrogen peroxide is reacting against to decide if it is being oxidised or reduced.

Remember:

H₂O₂ is reduced to H₂O

H₂O₂ is oxidised to O₂

Examples

H₂O₂ and KMnO₄

The MnO₄^- will be reduced so the H₂O₂ must be oxidised

H₂O₂ and KI

The I^- is oxidised so the H₂O₂ must be reduced

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with K₂Cr₂O₇?

• Reduced

• Oxidised

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with KMnO4?

• Reduced

• Oxidised

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with KCl?

• Reduced

• Oxidised

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with SO₂? (SO₂ --> SO₄^2-)

• Reduced

• Oxidised

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with Fe?

• Reduced

• Oxidised

Multiple Choice

Is the H₂O₂ reduced or oxidised when reacted with Br₂?

• Reduced

• Oxidised

Multiple Choice

When H₂O₂ is reduced, it is reduced into?

• O₂

• H₂O

Multiple Choice

When H₂O₂ is oxidised, it is oxidised into?

• O₂

• H₂O