What is the oxidation number of oxygen in water?

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Detailed Solution

The oxidation number (or oxidation state) of an element in a compound represents the hypothetical charge that atom would have if all bonds were purely ionic. To determine the oxidation number of oxygen in water (H₂O), we use the standard rules of oxidation states.

First, hydrogen usually has an oxidation number of +1 when bonded to nonmetals. Since water contains two hydrogen atoms, their combined oxidation number is +2.

Next, the overall charge of the water molecule is zero, as it is a neutral compound. Therefore, the sum of the oxidation numbers of all atoms must equal zero. Let the oxidation number of oxygen be x.

So, the equation becomes:

2(+1) + (x) = 0

2 + x = 0

x = -2

Thus, the oxidation number of oxygen in water is -2.

This value aligns with the general rule that oxygen typically has an oxidation state of -2 in most compounds, except in peroxides (where it is -1), superoxides (where it is -½), or when bonded to fluorine (where it can be positive).

Therefore, the oxidation number of oxygen in H₂O is -2.

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