Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    in HNO3, why does nitrogen have the oxidation state of +5 and not +3?

    Why does this occur and how do you know when it is in a +3 or +5 state?

    +rep too

    Thanks
    Offline

    10
    ReputationRep:
    The rules you need to know are oxygen nearly always has an oxidation state of -2 (if not a peroxide or superoxide). Hydrogen nearly always has an oxidation state of +1 (if not a hydride). In order to have an overall oxidation state of 0 (which all neutral molecules have) the nitrogen must be +5.
    Offline

    2
    ReputationRep:
    (Original post by Kyri)
    The rules you need to know are oxygen nearly always has an oxidation state of -2 (if not a peroxide or superoxide).
    Or if O is bonded with F, in which case it can have an oxidation number of +1 or +2. So all in all: O normally has -2, but this takes priority behind F having -1, H having +1 and the Group 1 metals having +1, so that in cases where you have only O and one of these 3 (F, H or a Group 1 metal) O can have a -1(peroxide) or -1/2 (superoxide) oxidation number.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Big-Daddy)
    Or if O is bonded with F, in which case it can have an oxidation number of +1 or +2. So all in all: O normally has -2, but this takes priority behind F having -1, H having +1 and the Group 1 metals having +1, so that in cases where you have only O and one of these 3 (F, H or a Group 1 metal) O can have a -1(peroxide) or -1/2 (superoxide) oxidation number.
    hi, so because in HNO3, the addition of oxygen is -6 (-2*3). but because hydrogen is always (or most times) +1, it goes down to -5, right?, therefore N would have to be +5 to get to 0, right.

    Note, is the oxidation state of oxygen in in HNO3 -6, or is it -2 (-6/3)?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Kyri)
    The rules you need to know are oxygen nearly always has an oxidation state of -2 (if not a peroxide or superoxide). Hydrogen nearly always has an oxidation state of +1 (if not a hydride). In order to have an overall oxidation state of 0 (which all neutral molecules have) the nitrogen must be +5.
    What do you mean by not a hydride?
    • Community Assistant
    • Study Helper
    Online

    15
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Hi, How are you ?)
    hi, so because in HNO3, the addition of oxygen is -6 (-2*3). but because hydrogen is always (or most times) +1, it goes down to -5, right?, therefore N would have to be +5 to get to 0, right.

    Note, is the oxidation state of oxygen in in HNO3 -6, or is it -2 (-6/3)?
    You don't take the sum of the atoms, you take the average. Oxygen is -2, as usual...
    Offline

    8
    ReputationRep:
    (Original post by Hi, How are you ?)
    in HNO3, why does nitrogen have the oxidation state of +5 and not +3?

    Why does this occur and how do you know when it is in a +3 or +5 state?

    +rep too

    Thanks
    In HNO3 the oxygen has a state of -2. There are 3 oxygens so you multiply the state by the three so oxygen is -6. The hydrogen has a +1 charge. When adding both states together you get -5. The overall charge on the molecule is 0 so you then know that the nitrogen is +5. Hope this makes sense!
    Offline

    10
    ReputationRep:
    (Original post by Hi, How are you ?)
    What do you mean by not a hydride?
    You can get compounds where the H is bonded directly to an alkali metal like NaH (sodium hydride) where the oxidation state of H is -1. I don't know if you'd encounter them in your course but I mentioned it as I predicted someone would come along and tell me that H isn't always +1.
    Offline

    2
    ReputationRep:
    (Original post by Hi, How are you ?)
    hi, so because in HNO3, the addition of oxygen is -6 (-2*3). but because hydrogen is always (or most times) +1, it goes down to -5, right?, therefore N would have to be +5 to get to 0, right.

    Note, is the oxidation state of oxygen in in HNO3 -6, or is it -2 (-6/3)?
    The oxidation number of an element in the compound is the average. So it's -2. That's what we meant when we said O usually has an oxidation number of -2: it doesn't matter how many there are, it'll always (usually) come out the same.

    As for thinking, yes, it's spot on. Short of calculating it properly, that's the same way I tend to think about it. e.g. Here's a tough example:

    [CuYAs3O6]2- - given that Cu has an oxidation number of +2 and Y has +4, what is the As oxidation number?

    Spoiler:
    Show
    You should get +(4/3). It's the average, remember.


    BTW, don't ask me anything about that ion's properties, I completely made it up just for this example!
    Offline

    1
    ReputationRep:
    (Original post by Hi, How are you ?)
    in HNO3, why does nitrogen have the oxidation state of +5 and not +3?

    Why does this occur and how do you know when it is in a +3 or +5 state?

    +rep too

    Thanks
    use algebra to find oxidation numbers

    H always has an ox number of +1 and O nearly always has one of -2

    Let N = x






    There Easy as that. Just gotta remember that Oxygen always has an Oxidation number of -2 (except in a few cases) and Hydrogen +1 and Group 1 metals +1 and group 2 metals +2!
    Offline

    1
    ReputationRep:
    the rifles of the iraaaaa
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.