[B9766]

I was following the discussion in the book regarding assignment of oxidation numbers up until the text said:
2Na(s) + 2H₂O(l)    2NaOH(aq) + H₂(g)
with oxidation numbers:
2Na(s) = 0
2H₂O(l) = +1
2NaOH = +1 and +1 for Na and OH respectively
H₂ = 0
I follow the assignment on 2Na (free element, oxi#=0), and H₂ (same rule).
But I can't see how H₂O = +1 or OH = +1


Following charge on H₂O, H oxi# should = 1+ and O oxi# should = 2- for a net of zero.
And the charge on OH would be O = 2- and H = 1+ for a net of 1-.


What am I getting wrong here?

[chenbeier]

You explained everything correct, there is nothing wrong. Oxidation numbers only assigned for elements and not for compounds.

The change of the charge is in Na 0 to Na⁺ +1 and H⁺ +1 to H₂ 0

Oxygen is in water and NaOH -2 and there is no change.

[B9766]

Sorry, I didn't understand the answer. Why would H20 have an oxidation number of +1?

[Borek]

Sorry, I didn't understand the answer. Why would H20 have an oxidation number of +1?

Not water, oxidation number is a property at a single atom, not of a molecule.

+1 for hydrogen (almost always) -2 for oxygen (almost always).