Question

Balance the half equation for this reaction to work out how many moles of electrons are needed to reduce one mole of nitrobenzene C6H5NO2+..........e- + ..........H+ = C6H5NH2+ .......H20?

Answer 1

You need six moles of electrons to reduce one mole of nitrobenzene.

Explanation:

You can find the general technique for balancing redox equations in acid solution here.

Step 1: Write the skeleton half-reaction.

`"C"_6"H"_5"NO"_2 → "C"_6"H"_5"NH"_2`

Step 2: Balance all atoms other than `"H"` and `"O"`.

Done.

Step 3: Balance `"O"`.

`"C"_6"H"_5"NO"_2 → "C"_6"H"_5"NH"_2 + "2H"_2"O"`

Step 4: Balance `"H"`.

`"C"_6"H"_5"NO"_2 + "6H"^"+" → "C"_6"H"_5"NH"_2 + "2H"_2"O"`

Step 5: Balance charge.

`"C"_6"H"_5"NO"_2 + "6H"^"+" + "6e"^"-" → "C"_6"H"_5"NH"_2 + "2H"_2"O"`

Step 6: Check mass balance.

`ulbb("Atom"color(white)(m)"On the left"color(white)(m)"On the right")`
`color(white)(ml)"C"color(white)(mmmmml)6color(white)(mmmmmmll)6`
`color(white)(ml)"H"color(white)(mmmmll)11color(white)(mmmmmml)11`
`color(white)(ml)"N"color(white)(mmmmml)1color(white)(mmmmmmll)1`
`color(white)(ml)"O"color(white)(mmmmml)2color(white)(mmmmmmll)2`

Step 9: Check charge balance.

`mathbf("On the left"color(white)(m)"On the right")`
`color(white)(mmm)0color(white)(mmmmmmll)0`

∴ The balanced half-reaction is

`"C"_6"H"_5"NO"_2 + "6H"^"+" + "6e"^"-" → "C"_6"H"_5"NH"_2 + "2H"_2"O"`

The reduction half-reaction involves six moles of electrons.