# Confusion with Law of Equivalence

Law of equivalence states that

One equivalent of an element combines with one equivalent of the other.

Equivalent of $\ce{Na}$ is $22.99$ and that of $\ce{O}$ is $8$. By the law of equivalence, $1$ equivalent of $\ce{Na}$ combines with $1$ equivalent of $\ce{O}$. But in $\ce{Na2O2}$, $$23 \times 2 ~\text{parts by weight of sodium combines with } 16 \times 2~\text{parts by weight of oxygen} \\\implies 23~\text{parts by weight of sodium combines with } 16~\text{parts by weight of oxygen}$$ which means one equivalent of sodium combines with two equivalents of oxygen which is contradiction to law of equivalence. So why does this compound not follow the law of equivalence?

$\ce{Na_2O_2}$ is sodium peroxide. It contains oxygen (normally a very well behaved element, chemically speaking) behaving in an unusual way, bonding not only with sodium but also with another oxygen atom. The oxygen can be thought of as part of a peroxide ion, $\ce{O2^2-}$.
• Sir,what is the equivalent of sodium in sodium peroxide? My book says sodium doesn't exhibit variable equivalent weight so eq.wt of $\ce{Na}$ is $23$ . But to me, it is $11.5$ . Which is right? – user5764 Oct 22 '14 at 4:45