In this post, we will determine the oxidation numbers in hydrogen peroxide, H₂O₂.

To determine the oxidation number of an atom(s) in a molecule or an ion, start with the known oxidation numbers and the rules summarized below:

 

 

Keep in mind that the summary is zero for neutral molecules and is equal to the charge for ions.

For H₂O₂ the element with a standard oxidation state is hydrogen which is +1, and we need to determine the oxidation state of the oxygen. 

Rule 6 – The oxidation of hydrogen is +1:

Assign x for the oxidation state of O and set up an equation:

 

2(+1) + 2x = 0,  x = -1

This is an unusual oxidation number of oxygen in a molecule, and the reason is that the two oxygens are connected, so they each pull the electron density only from one hydrogen atom:

We discussed the Lewsis structure and hybridization of H₂O₂ in a separate article which you can find here. 

 

Further Reading

• Solutions
• Strong and Weak Electrolytes
• Dissociation of Ionic Compounds
• Molecular, Ionic, and Net Ionic Equations
• Molarity 
• Dilution
• Ion Concentration
• Precipitation Reactions
• Definitions of Acids and Bases
• Naming Acids and Bases
• Acid-Base Reactions
• Displacement Reactions
• Predicting The Products of Chemical Reactions
• Stoichiometry of Reactions in Aqueous Solutions
• Acid-Base Titrations
• Oxidation State
• Oxidation-Reduction (Redox) Reactions
• Balancing Redox Reactions
  Reactions in Aqueous Solutions – Practice Problems

 

More examples of the oxidation state in this multiple-choice quiz: