Hey there! Sign in to join this conversationNew here? Join for free

Redox question Watch

Announcements
    • Thread Starter
    Offline

    18
    ReputationRep:
    Hi guys, i'm a bit stuck... i don't understand how to calculate 3 electrons. At the moment, I understand that 4 Hydrogens on the left has an oxidation state of +1.
    NO3- has an oxidation state of -1, and NO has an oxidation state of +2 and H2O has an oxidation state of 0. But where did 3 electrons come from..? I calculated.. 2 electrons on the left hand side.

    NO3−+ 4H++ 3e→ NO + 2H2O
    Offline

    2
    ReputationRep:
    Electrons are used to balance charge. Since there is no overall charge on the right hand side, the sum of the charges on the left must also equal 0. There are 4 H+ and one NO3-, so without any electrons there is an overall charge of +3. Therefore 3 electrons are needed to make the overall charge of the left hand side 0.
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by MKaur18)
    Hi guys, i'm a bit stuck... i don't understand how to calculate 3 electrons. At the moment, I understand that 4 Hydrogens on the left has an oxidation state of +1.
    NO3- has an oxidation state of -1, and NO has an oxidation state of +2 and H2O has an oxidation state of 0. But where did 3 electrons come from..? I calculated.. 2 electrons on the left hand side.

    NO3−+ 4H++ 3e→ NO + 2H2O
    You are a little confused with how you are using oxidation states. Compounds and ions do not have an oxidation state. It is the elements themselves that are assigned oxidation states.

    NO3- is an ion in which the oxidation state/number of the nitrogen atom is +5. Each of the oxygen atoms has an oxidation number of -2.

    If you look at the equation above you can see that nitrogen atoms on the LHS change from oxidation state +5 to oxidation state of +2 on the RHS.

    No other element changes oxidation state.

    The nitrogen atom must accept 3e to go from +5 to +2.

    The final equation must be balanced in terms of atoms AND charge (as the poster above stated). You can use this as a "checksum" to test your answer.
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by charco)
    You are a little confused with how you are using oxidation states. Compounds and ions do not have an oxidation state. It is the elements themselves that are assigned oxidation states.

    NO3- is an ion in which the oxidation state/number of the nitrogen atom is +5. Each of the oxygen atoms has an oxidation number of -2.

    If you look at the equation above you can see that nitrogen atoms on the LHS change from oxidation state +5 to oxidation state of +2 on the RHS.

    No other element changes oxidation state.

    The nitrogen atom must accept 3e to go from +5 to +2.

    The final equation must be balanced in terms of atoms AND charge (as the poster above stated). You can use this as a "checksum" to test your answer.
    Ohh, i understand now. Thank you so much.
    The mark scheme said NO^3- which confused me even more before. I get it now! So it's to do with the oxidation state which changes and the difference in between 🙈 Aaaah. Wish i knew that sooner.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Break up or unrequited love?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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