Chapter 4
Q. 4.7
Consider the unbalanced redox equation:
Cr^{3+}(aq) + H_{2}O_{2}(aq) → 2H_{2}O + Cr_{2}O_{7}^{2-}(aq)
(a) Identify the element oxidized and the element reduced.
(b) What are the oxidizing and reducing agents?
STRATEGY
1. Determine the oxidation number of each element.
2. Find elements whose oxidation numbers change.
Step-by-Step
Verified Solution
| Cr: +3; H: +1; O: -1 → H: +1; O: -2; Cr: +6 | Oxidation numbers |
| Cr: +3 → +6 (increase)
O: -1 → -2 (decrease) |
Change |
| O (decrease in oxidation number) | Element reduced |
| Cr (increase in oxidation number) | Element oxidized |
| H_{2}O_{2} (It is the species that contains the element that is reduced.) | Oxidizing agent |
| Cr_{2}O_{7}^{2-} (It is the species that contains the element that is oxidized.) | Reducing agent |