Oxidation-Reduction

  4) (a)

                  +3 -3          +2  -2                  +3 +3 -6

                        -1          +1  -2                  +1      -2         +1 -1

               PBr₃ + 3H₂O H₃PO₃ + 3HBr

               This is not an oxidation-reduction reaction because there is no change in oxidation states.

      (b)

                                                                 +1 +5 -6

                   +1 -1       +1 -2 +1                          -2         +1 -1

               NaI + 3HOCl NaIO₃ + 3HCl

                                             -1               +5                                                     +1                   -1

               oxidation:   I I                    reduction:   Cl Cl

      (c)

                     +4 -4         +1+5-6         +2 -2                      +2 +6-8

                           -2                  -2         +1 -2                      +1      -2       +2 -2                

               3SO₂ + 2HNO₃ + 2H₂O 3H₂SO₄ + 2NO

                                            +4               +6                                                     +5                +2

               oxidation:   S S                     reduction:   N N

      (d)

                     +2 +6 -8                                                    +4 -4      +2  +6 -8          +2  -2

                     +1       -2         +1   -1                      0             -2      +1        -2         +1  -2            

               2H₂SO₄ + 2NaBr Br₂ + SO₂ + Na₂SO₄ + 2H₂O

                                               -1                   0                                                        +6               +4

               oxidation:   Br Br₂                     reduction:   S S