4.6: Answers to Practice Problems

4.1.1. Identifying oxidation states.

A. \(\text{NH}_{4}^{+} \ (\text{N} = -3)\), \(\text{N}_{2} \ (\text{N} = 0)\), \(\text{NO}_{3}^{-} \ (\text{N} = +5)\), \(\text{NO}_{2}^{-} \ (\text{N} = +3)\)

B. \(\text{CHOO}^{-} \ (\text{C} = +2)\), \(\text{CHOOH} \ (\text{C} = +2)\), \(\text{CH}_{4} \ (\text{C} = -4)\), \(\text{CO}_{2} \ (\text{C} = +4)\)

4.1.2. Identifying redox reactions.

A. Not redox

B. Redox with \(\text{N}\) in \(\text{NO}_{3}^{-}\) reduced and \(\text{H}\) in \(\text{H}_{2}\) oxidized

C. Redox with \(\text{As}\) in \(\text{H}_{2} \text{AsO}_{4}^{-} reduced and \(\text{C}\) in \(\text{HCOO}^{-}\) oxidized

D. Not redox

4.2.1. Balancing redox reactions.

1. \(8 \ \text{Fe(OH)}_{3} \ (s) + 15 \ \text{H}^{+} + \text{CH}_{4} \longrightarrow 21 \ \text{H}_{2} \text{O} + 8 \ \text{Fe}^{2+} + \text{HCO}_{3}^{-}\)
2. \(\text{H}^{+} + \text{CH}_{4} + \text{SO}_{4}^{2-} \longrightarrow \text{H}_{2} \text{S} + \text{H}_{2} \text{O} + \text{HCO}_{3}^{-}\)
3. \(3 \ \text{H}_{2} + 2 \ \text{H}^{+} + 2 \ \text{NO}_{2}^{-} \longrightarrow \text{N}_{2} + 4 \ \text{H}_{2} \text{O}\)
4. \(\text{NH}_{4}^{+} + 2 \ \text{O}_{2} \longrightarrow \text{H}_{2} \text{O} + 2 \ \text{H}^{+} + \text{NO}_{3}^{-}\)
5. \(\text{NH}_{4}^{+} + 1.5 \ \text{O}_{2} \longrightarrow \text{H}_{2} \text{O} + 2 \ \text{H}^{+} + \text{NO}_{2}^{-}\)
6. \(\text{NH}_{4}^{+} + \text{NO}_{2}^{-} \longrightarrow 2 \ \text{H}_{2} \text{O} + \text{N}_{2}\)
7. \(8 \ \text{Fe(OH)}_{3} \ (s) + 14 \ \text{H}^{+} + \text{H}_{2} \text{S} \longrightarrow 20 \ \text{H}_{2} \text{O} + 8 \ \text{Fe}^{2+} + \text{SO}_{4}^{2-}\)

4.4.1. Respiration and fermentation.

1. Fermentation
2. Fermentation
3. Fermentation
4. Fermentation
5. Respiration
6. Respiration

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