Chapter 19, Problem 29P

Interpretation Introduction

Interpretation:

Oxidation and reduction reactions should predict to complete the overall mechanism.

Concept introduction:

The formation of oxygen in the light dependent step of the photosynthesis was proved by the Hill reaction. Hill reaction is composed of an oxidation and reduction steps.

Oxidation reaction takes place by removing electrons to get a larger oxidation number to an atom. Consider oxygen in H₂O and O₂. Both are neutral. Therefore, the total charge of water and oxygen is zero.

H+ in water has $+1$ charge. Therefore, H oxidation number in water = $+1$

Assume oxygen’s oxidation number as $x$ in H₂O.

$\begin{array}{l}\left(+2\right)+\left(x\right)=0\\ x=-2\end{array}$

Assume Oxygen’s oxidation number in O₂as $y.$

$\begin{array}{l}2y=0\\ y=0\end{array}$

${\text{H}}_{\text{2}}\text{O }\to {\text{ O}}_{\text{2}}$

$\left(-2\right)$

$\left(0\right)$

Oxidation number of oxygen has increased. Therefore, an oxidation reaction is taking place.

Likewise, reduction is the lowering of oxidation number of a particular atom.

${\left({\text{Fe}}^{+3}{\left(\text{CN}\right)}_6\right)}^{-3}\to {\left({\text{Fe}}^{+2}{\left(\text{CN}\right)}_6\right)}^{-4}$

The oxidation number of Fe has been reduced from $+3$ to $+2$. Therefore, a reduction reaction takes place.