How do we find the oxidation number of an element?

Answer 1

For an element, the oxidation number is easy to assign.......

The oxidation number of any element is #0#. We assign oxidation numbers on the basis of the number of electrons donated (#"oxidation"#), or the number of electrons accepted (#"reduction"#).

Of course these designations are completely conceptual, nevertheless, these ideas are useful for writing and balancing redox reactions. We consider here the oxidation of iodine to periodate ion, #IO_4^-#. Now the oxidation number of oxygen in its compounds is generally #-II# and it is so here. Thus the oxidation number of iodine in periodate is #VII+#, the Group oxidation number.

On the other hand, elemental iodine, has neither accepted nor donated electrons, and its oxidation state is formally #"zero"#.

#1/2I_2 + 4H_2O rarr IO_4^(-) + 8H^(+) +7e^-#

This is just the oxidation half of the equation; something (oxygen?) has to be reduced.

For combustion reactions, we can write a complete redox reaction as follows:

#C(s) +O_2(g) rarr CO_2(g)#

Elemental (and zerovalent) carbon is oxidized to #C(IV+)#. Elemental oxygen is oxidized to #O(-II)#. Formally, how many electrons have been transferred in this reaction?

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Answer 2

Wyatt Adkins

To find the oxidation number of an element, follow these steps:

Determine the common oxidation states for the element.
Identify the oxidation state of known elements in the compound or ion.
Apply the rules for assigning oxidation numbers, such as:
- The oxidation number of an element in its elemental form is zero.
- In compounds, hydrogen usually has an oxidation number of +1 and oxygen usually has an oxidation number of -2.
- The sum of oxidation numbers in a neutral compound is zero, and in a polyatomic ion, it equals the charge of the ion.
Use algebraic manipulation to find the oxidation number of the unknown element.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.