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Balance the following redox equation: ...

Balance the following redox equation:
`(i) Cu+NO_(3)^(-)rarrrNO_(2)+Cu^(2+)`(Acidic medium)
`(ii) [Cr(OH)_(4)]^(-)+H_(2)O_(2)rarrrCrO_(4)^(2-)+H_(2)O`(Basic medium)
`(iii) MnO_(4)^(-)+Fe^(2+)rarrMn^(2+)+Fe^(3+)+H_(2)O`(Acidic medium)

Text Solution

Verified by Experts

`(i)Cu+NO_(3)^(-)rarrNO_(2)r+Cu^(2+)`(Acidic medium)
1. Write the O.N of each atom in the skeleton `eqution^(*)`
`overset(0)Cuoverset(+5)(Noverset(-2)O_(3))rarroverset(+4)Noverset(2)O_(2)+overset(+2)(Cu)^(2+)`
2.Identify the atoms which undergo change in O.N
`overset(0)Cu+overset(NO_(3)^(-))rarrroverset(+4)NO_(2)+overset(+2)(Cu)^(2+)`
3. Calculate the increase and decrease in O.N w.r.t to reactant atoms

4.Equate the increase and decrease in O.N on the reactant side .
`Cu+2NO_(3)^(-)rarrNO_(1)+Cu^(2+)`
5.Balance the number of Cu and N atoms on both sides of the equation
`Cu+2NO_(3)^(-)rarr2NO_(2)+Cu^(2+)`
6. As the reaction is carried in the acidic medium b alance the number of O atoms by adding two `H_(2)O` molecules on the product side
`Cu+2NO_(3)^(-)rarr2NO_(2)+Cu^(2+)+2H_(2)O`
7. "To balance the number of H atoms add" `4H^(+)` "on the reactant side"
`Cu+2NO_(3)^(-)+4H^(+)rarr 2NO_(2)Cu^(2+)+2H_(2)O`
"The final equation is balacned w.r.t charges also."
`(ii) [Cr(OH)_(4)]^(-)+H_(2)O_(2)rarrCrO_(4)^(2-)+H_(2)O` (Basic Medium)
"The balancing is done in the following steps":
"1.Write the O.N of each atom in the skeleton equation"
`overset(+3)[Croverset(-2)(Ooverset(+1)H)_(4)]+overset(+1)H_(2)overset(-1)O_(2)rarroverset(+6)(Coverset(-2)O_(4))+overset(+1)+H_(2)overset(-2)O`
2."Identify the atoms which undergo change in O.N"
"3.Calculate the increase and decerease in O.N w.r.t reactant astoms"

"4.Equate the increase and decrease in O.N in the reactant side."
`2[Cr(OH)_(4)]^(-)+3H_(2)O_(2)rarr(CrO_(4))^(2-)+H_(2)O`
`(iii) MnO_(4)^(-) +Fe^(2+)rarrMn^(2+)+Fe^(3+)+H_(2)O` (Acidic medium)
"The balancing is done in the following steps:"
"1.write the O.N of each atoms in the skeleton equation"
`overset(+7)Mnoverset(-2)O_(4)^(-)+overseT(+2)(Fe)^(2+)rarroverset(2+)(Mn)^(2+)+overset(+3)(Fe)^(3+)+overset(+1)H_(2)overset(-2)O`
"2.Identify the atoms which undergo change in O.N"
`overset(+7)(Mnoverset(-2)O_(4))+overset(+2)(Fe)^(2+)rarroverset(+2)(Mn)^(2+)+overset(+3)(Fe)^(3+)+H_(2)O`
"3.Calaculate the increase and decrease in O.N w.r.t reactant atoms."

"4 Equate the increase and decrease in O.N on the reactant side"
`MnO_(54)^(-)+5Fe^(2+)rarrMn^(2+)+Fe^(3+)+H_(2)O`
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