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### Topic: Finding the oxidation number of N in KNO2  (Read 2162 times)

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#### kstervic

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##### Finding the oxidation number of N in KNO2
« on: September 06, 2014, 06:44:28 PM »
Hi I am having some trouble with one particular question.
The question is: What is the oxidation number for the atom N is KNO2?
This is the explanation I got.

It looks like we have 2 unknown oxidation numbers (K & N), but the truth is that there is only one unknown (N).  This is because KNO2 is a polyatomic (because it is called potassium nitrite, & nitrite is a polyatomic ion).  Since polyatomic molecules are ionic, this means we know that the oxidation number of K must be +1 by the uncriss-crossing rule.  We then look at O & its oxidation number is -2.  The molecule is neutral, so the algebraic expression equals 0.  We then solve as usual.

I understand every line of that explanation except how we find the oxidation number of K.
How do we use the uncriss-crossing rule to find that K has a charge of +1?

#### Borek

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##### Re: Finding the oxidation number of N in KNO2
« Reply #1 on: September 07, 2014, 03:37:12 AM »
One of the basic rules when assigning oxidation numbers is that alkali metals (Li, Na, K, Rb, Cs) are always +1.

What they probably mean is that NO2- is known to be -1 as a group, so potassium must be K+ (or +1).
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#### Partha Sarker

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##### Re: Finding the oxidation number of N in KNO2
« Reply #2 on: September 11, 2014, 02:53:19 AM »
It will be +3