The Oxidation State of Nitrogen Is Most Positive In Which Compound?

The Oxidation State of Nitrogen Is Most Positive In Which Compound?

This is an SAT Chemistry question from 1998 SAT Chemistry test.

a. NO3^-1

b. NO2^-1

c. N2O

d. N2

e. NH3

Answer and Explanation:

Lets first go over some rules for assigning the oxidation number.

• Free element has an oxidation number of 0. For example, O2, Fe, Cl2 etc all have oxidation numbers of zero. Therefore, nitrogen in choice d has an oxidation number of 0

• All oxidation numbers in a neutral compound add up to 0. For example, lets solve N2O. Oxygen has an oxidation number of -2 as can be seen on the periodic table (group 16 is mostly -2 oxidation number). Lets now make an equation since we dont know nitrogen, we will make it x. 2x+ (-2) = 0. Therefore, x=+1. Let's solve choice e the same way. Hydrogen is +1 unless with a metal. Thus, we get x+1*3=0, x= -3. Choice e can be eliminated.

• All oxidation number of a charged compound must add up to its charge. Lets now solve choices a and b. Choice a's equation becomes x+(-2*3)= -1 x=+5 Choice b is x+(-2*2)= -1 x=+4. We can now see that choice A must be the correct answer since it gave us positive five charge for the nitrogen.

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