NEED HELP ASAP! how do I balance these 3 redox equations.?

1) Mno4 -1 + SO3 2- ---> MnO4 2- + SO4 2-

2) Cr2O7 2- + SO3 2- ---> Cr 3+ + SO4 2-

3) Cu + HNO3 --> Cu(NO3)2 + NO2

if you know how to answer any of these, it would be greatly appreciated!

1 Answer

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  • Paul
    Lv 4
    6 years ago
    Best Answer

    Easiest using oxidation numbers

    Manganese goes from +7 to +6 a change of -1

    Sulphur goes from + 4 to + 6 a change of + 2

    so twice as many Manganese atoms must change as Sulphur

    2MnO4 - + SO3 2- -> 2 MnO4 2- + SO4 2-

    now check Os ; there is one more on RHS so add H2O to LHS and 2H+ to RHS.

    2MnO4 - + SO3 2- + H2O -> 2 MnO4 2- + SO4 2- + 2H+

    As a check show that charges balance : 4- and 4- : done.

    Copper goes from 0 to + 2

    Nitrogen goes from +5 to +4 (in NO2, NO3- is still +5)

    so 2 Nitrogens change per copper (but there are 2 unchanged in copper nitrate)

    Cu + 4 HNO3 -> Cu(NO3)2 + 2NO2

    there are 4 Hs and 2Os to account for - that is 2H2O

    Cu + 4 HNO3 -> Cu(NO3)2 + 2NO2 + 2H2O

    OK ?

    Source(s): for oxidation nunbers see eg http://www.chemguide.co.uk/inorganic/redox/oxidnst...
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