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Balance the following ionic equations (i) Cr_2O_7^(2-) +H^(+)I^(-) rarr Cr^(3+)+I_(2)+H_(2)O (ii) Cr_2O_(7)^(2-) +Fe^(2+)+H^(+)rarrCr^(3+)+Fe^(3+)+H_2O (iii) MnO_(4)^(-) +SO_(3)^(2-)+H^(+)rarrMn^(2+)+SO_4^(2-)+SO_(4)^(2-)+H_2O (iv) MnO_(4)^(-) +H^(+)+Br^(-) rarr Mn^(2+)+Br_(2)+H_(2)O |
Answer» Solution :(i)  Dividing the equation into two HALF reactions : Oxidation half reaction : `I^(-) rarrI_(2)` REDUCTION half reaction : `Cr_(2)O_(7)^(2-) rarrCr^(3+)` Balancing oxidation and reduction half reactions separately as : Oxidation half reaction `I^(-) rarr I_2` `2I^(-) rarr I_2` `2I^(-) rarr I_2+2e^(-) ""...(i)` Reduction half reaction `Cr_(2)O_(7)^(2-) rarr Cr^(3+)` `Cr_(2)O_(7)^(2-)rarr2Cr^(3+)` `Cr_2O_(7)^(2-) +6e^(-) rarr 2Cr^(3+)+7H_2O""...(ii)` `""("acidic medium")` To balance the electronsmultiply eq(i) by 3 and add to eq (ii) `Cr_(2)O_(7)^(2-) +14H^(+)+6I^(-) rarr 2Cr^(3+)+3I_(2)+7H_2O` (iii)  Dividing the equation into two half reactions : Oxidation half reaction : `SO_(3)^(2-) rarr SO_(4)^(2-)` Reduction half reaction : `MnO_(4)^(-) rarr MN^(2+)` Balancing oxidation and reduction half reactions separately as : Oxidation half reation `SO_(3)^(2-) rarr SO_4^(2-)` `SO_3^(2-) rarr SO_(4)^(2-) +2e^(-)` Since the reaction occurs in acidic medium, `SO_3^(2-) rarr SO_4^(2-) +2e^(-) +2H^(+)` `SO_3^(2-) +H_2O rarr SO_4^(2-) +2H^(+) +2e^(-) .....(i)` Reduction half reaction `MnO_4^(-) rarr Mn^(2+)` `MnO_4^(-) +5e^(-) rarr Mn^(2+)` `MnO_4^(-) +8H^(+) +5e^(-) rarr Mn^(2+)` `MnO_4^(-) +8H^(+) +5e^(-) rarr Mn^(2+) +4H_2O""....(ii)` To balance the electrons , multiply eq. (i) by 5 and eq (ii)by 2 and add `2Mn_4^(-) +5SO_(3)^(2-) +6H^(+) rarr 2Mn^(2+)+5SO_4^(2-) +3H_2O` (IV)  Dividing the equation into two half reactions : Oxidation half reaction : `Br^(-) rarr Br_2` Reduction half reaction : `MnO_4^(-) rarr Mn^(2+)` Balancing oxidation and reduction half reaction separately as : Oxidation half reaction `Br^(-) rarr Br_2` `2Br^(-) rarr Br_2` `2Br^(-) rarr Br_2+2e^(-) ""...(i)` Reduction `MnO_4^(-) rarr Mn^(2+)` `MnO_4^(-) +5e^(-) rarr Mn^(2+)` `MnO_4^(-) +8H^(+) +5e^(-) rarr Mn^(2+)` `MnO_4^(-) +8H^(+) +5e^(-) rarr Mn^(2+)+4H_2O""...(ii)` To balance the electrons, multiply eq (i) by 5 and eq (ii) by 2 and add `2MnO_4^(-) +10Br^(-) +16 H^(+) rarr 2Mn^(2+)+5Br_2+8H_2O` |
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