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    • Thread Starter

    hi just doing chem revition and cant under stand this bit (if you have the 2nd editon chemical ideas book its page 205-206 9.1)

    ok it says that for H20 the oidaqtion states of the elements is h+1 and for o-2
    which makes sence since the oxidation state of a compound = O and (2x1)-2=0

    How ever in the first example it gives the oxidation state of CO2 ass follows

    oidation state of O = -2 x 2 =-4 (simple mathmatics)
    then this is where i get confused it states that the oxidation state of C = -4 also and follows up to say that theis shows the compund has a oxidation state of 0 but is that rightwouldnt it be -8 if they said C was -4 so wat im saying is isnt C supposed to be +4.

    I thought it must of been a mistake but the snd example also gives an equation where you have 2 negative numbers instead of a postive and a negative (that i showed in the H20 bit)

    please help im confused lol

    cheers mark
    • Community Assistant
    • Study Helper

    Community Assistant
    Study Helper
    The oxidation state of carbon in CO2 is +4
    oxygen is highly electronegative and therefore any element bonded to it (except fluorine) has to be in the positive oxidation state.
    This rule works for all combinations of elements.
    NH3 the nitrogen is negative -3 as it's more electronegative than hydrogen
    NO2 the nitrogen is positive +4 as it's less electronegative than oxygen.
    etc etc

    Read your text?
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