# Question 06291

May 5, 2017

Here's the balanced equation for the first question:

$\text{2I"^"-" + "NiO"_2 + 2"H"_2"O"→ "I"_2 + "Ni(OH)"_2 + 2"OH"^"-}$

#### Explanation:

You can find the detailed procedure here.

The skeleton equation is

${\text{I"^"-" + "NiO"_2 → "I"_2 +"Ni(OH)}}_{2}$

1. Half-reactions

${\text{I"^"-" → "I}}_{2}$
${\text{NIO"_2 → "Ni(OH)}}_{2}$

2. Balance all atoms other than $\text{H}$ and $\text{O}$

$\textcolor{red}{2} {\text{I"^"-" → color(red)(1)"I}}_{2}$
$\textcolor{b l u e}{1} {\text{NiO"_2 → color(blue)(1)"Ni(OH)}}_{2}$

3. Balance O

Done.

4. Balance $\text{H}$

$\textcolor{red}{2} {\text{I"^"-" → color(red)(1)"I}}_{2}$
$\textcolor{b l u e}{1} {\text{NiO"_2 +color(olive)(2)"H"^"+" → color(blue)(1)"Ni(OH)}}_{2}$

5. Balance electrons

$\textcolor{red}{2} \text{I"^"-" → color(red)(1)"I"_2 + color(orange)(2)"e"^"-}$
$\textcolor{b l u e}{1} {\text{NiO"_2 +color(olive)(2)"H"^"+" + color(orange)(2)"e"^"-" → color(blue)(1)"Ni(OH)}}_{2}$

6. Equalize electrons transferred

1 × [color(red)(2)"I"^"-" → color(red)(1)"I"_2 + color(orange)(2)"e"^"-"]
1 × [color(blue)(1)"NiO"_2 +color(olive)(2)"H"^"+" + color(orange)(2)"e"^"-" → color(blue)(1)"Ni(OH)"_2]

1 × [color(red)(2)"I"^"-" → color(red)(1)"I"_2 + color(red)(cancel(color(black)(color(orange)(2)"e"^"-")))]
1 × [color(blue)(1)"NiO"_2 +color(olive)(2)"H"^"+" + color(red)(cancel(color(black)(color(orange)(2)"e"^"-"))) → color(blue)(1)"Ni(OH)"_2]
stackrel(——————————————————)(color(red)(2)"I"^"-" + color(blue)(1)"NiO"_2 + color(olive)(2)"H"^"+" → color(red)(1)"I"_2 + color(blue)(1)"Ni(OH)"_2)

8. Convert to base

$\textcolor{red}{2} {\text{I"^"-" + color(blue)(1)"NiO"_2 + color(red)(cancel(color(black)(color(olive)(2)"H"^"+"))) → color(red)(1)"I"_2 + color(blue)(1)"Ni(OH)}}_{2}$
$2 \text{H"_2"O" →color(red)(cancel(color(black)(2"H"^"+"))) + 2"OH"^"-}$
stackrel(————————————————————)(color(red)(2)"I"^"-" + color(blue)(1)"NiO"_2 + 2"H"_2"O"→ color(red)(1)"I"_2 + color(blue)(1)"Ni(OH)"_2 + 2"OH"^"-")#

The balanced equation is

$\text{2I"^"-" + "NiO"_2 + 2"H"_2"O"→ "I"_2 + "Ni(OH)"_2 + 2"OH"^"-}$

Now, can you use the same method to balance the second equation?