Choose the item that correctly describes the oxidizing agent and the reducing ag
ID: 1006252 • Letter: C
Question
Choose the item that correctly describes the oxidizing agent and the reducing agent in the reaction shown. Cr2O3(s) + 3CO(g) 2Cr(s) + 3CO2(g)
A. C changes from oxidation number +2 to +4. The CO is the reducing agent. Cr changes from oxidation number +3 to +2. The Cr2O3 is the oxidizing agent.
B. C changes from oxidation number +2 to +4. The CO is the reducing agent. Cr changes from oxidation number +2 to +3. The Cr2O3 is the oxidizing agent.
C. C changes from oxidation number +2 to +4. The CO is the reducing agent. Cr changes from oxidation number +3 to 0. The Cr2O3 is the oxidizing agent.
D. C changes from oxidation number +4 to +2. The CO is the reducing agent. Cr changes from oxidation number +3 to 0. The Cr2O3 is the oxidizing agent.
PART B
Choose the item that correctly describes the oxidizing agent and the reducing agent in the reaction shown. PbS(s) + 4H2O2(aq) PbSO4(s) + 4H2O()
A. S changes from oxidation number -2 to +6. The PbS is the reducing agent. O changes from oxidation number -1 to -2. The H2O2 is the oxidizing agent.
B. S changes from oxidation number -2 to +4. The PbS is the reducing agent. O changes from oxidation number -1 to -2. The H2O2 is the oxidizing agent.
C. S changes from oxidation number +2 to +6. The PbS is the reducing agent. O changes from oxidation number -1 to -2. The H2O2 is the oxidizing agent.
D. S changes from oxidation number -2 to +6. The PbS is the oxidizing agent. O changes from oxidation number -1 to -2. The H2O2 is the reducing agent.
Explanation / Answer
In the first part:
Cr2O3 (s) + 3CO (g) 2Cr (s) + 3CO2 (g)
In Cr2O3 chromium has oxidation number +3 which is reduced by CO to elemental chromium of oxidation number zero. Whereas in CO carbon has oxidation number +2 which is oxidized to CO2 by Cr2O3 having oxidation number of carbon +4. Here Cr2O3 is oxidizing agent and CO is educing agent.
The answer is (C)
In the second part:
PbS (s) + 4H2O2 (aq) PbSO4 (s) + 4H2O ()
Here sulphide in PbS has oxidation number -2 is oxidized to sulphate by peroxide having oxidation number of sulfur +6. Whereas oxygen in peroxide has oxidation number -1 is reduced to oxide having oxidation number -2 by sulphide. Here peroxide is oxidizing agent and suphide is reducing agent.
The answer is (A)