Chapter 18, Problem 6A

Interpretation Introduction

Interpretation: The reason for oxidation state of O to be -2 in H₂O needs to be explained. Also, an example of a compound in which oxygen is not in the -2 oxidation state needs to be identified.

Concept introduction: Oxidation state is the concept which explains the gain or loss of electrons in oxidation−reduction reactions.

Explanation of Solution

Water $\left({\text{H}}_{\text{2}}\text{O}\right)$ has no ions. It is as covalent compound. The charge assigned to an element in the compound tells about its oxidation state. Most of the electronegative atoms control both the shared pair of electrons in the bond. Thus, electrons in O-H bond of water are controlled by electronegative atom. Thus, O gets partial negative and H gets partial positive charge. Peroxide $\left({\text{O}}_2{}^{2-}\right)$ has two oxygen atoms and they are linked together by single covalent bond. In peroxide, oxidation state of oxygen is -1.

Conclusion

Thus, peroxide is a compound that has O with oxidation state -1.