Chapter 19.2, Problem 21PP

Interpretation Introduction

Interpretation:

The given redox reaction is to be balanced using oxidation number method.

Concept introduction:

Oxidation number method to balance ionic equation in acidic solution involve:-

• Assign the oxidation number to each element.
• Check which element is oxidized and which element is reduced.
• Check the change in oxidation number for the elements which are oxidized and reduced.
• Balance the change in oxidation number by adjusting the coefficients in the equation.
• Then add enough hydrogen ions and water molecules to the equation to balance hydrogen atoms on both sides.

Answer to Problem 21PP

$Zn+2N{O}_3{}^{-1}+4H^{+}\to Z{n}^{+2}+2N{O}_2+2H_{2}O$

Explanation of Solution

The given redox reaction is:

$Zn+N{O}_3{}^{-1}\to Z{n}^{+2}+N{O}_2$

Assigning the oxidation number-

$\stackrel{0}{Zn}+\stackrel{+5}{N}{\stackrel{-2}{O}}_3{}^{-1}\to \stackrel{+2}{Z{n}^{+2}}+\stackrel{+4}{N}{\stackrel{-2}{O}}_2$

The oxidation numbers of atoms shows that

$Zn$ is oxidized and $N$ is reduced.

Change in oxidation number of $Zn=+2$

Change in oxidation number of $N=-1$

Thus adjusting the coefficients:

$Zn+2N{O}_3{}^{-1}\to Z{n}^{+2}+2N{O}_2$

Now adding hydrogen ions on left side of equation to balance negative charge

$Zn+2N{O}_3{}^{-1}+4H^{+}\to Z{n}^{+2}+2N{O}_2$

Adding water to right side:

$Zn+2N{O}_3{}^{-1}+4H^{+}\to Z{n}^{+2}+2N{O}_2+2H_{2}O$

Conclusion

Thus the balanced redox equation is:

$Zn+2N{O}_3{}^{-1}+4H^{+}\to Z{n}^{+2}+2N{O}_2+2H_{2}O$