Chemistry - Redox Reactions Question with Solution | TestHub
A set of metallurgical and redox reactions are listed below.
Determine the total of all oxidation states of the different metallic elements present in the final products of these processes:
Zn + NaOH(aq), (NH₄)₂Cr₂O₇ (strong heating),
Molten Al₂O₃ (electrolysis), Au + O₂ + KCN(aq), K₂Cr₂O₇ in basic medium.
Calculate the final numerical value.
Answer:
Solution:
1. Zn + NaOH → Na₂[Zn(OH)₄]
Zn in sodium zincate → +2
2. (NH₄)₂Cr₂O₇ (strong heating) → Cr₂O₃
Cr in Cr₂O₃ → +3
3. Molten Al₂O₃ (electrolysis) → Al
Al → 0
4. Au + O₂ + KCN → [Au(CN)₂]⁻
Au → +1
5. K₂Cr₂O₇ in basic medium → K₂CrO₄
Cr already counted from Cr₂O₃; do not count again
Only different metals are counted once. If a metal appears in multiple products, we consider the oxidation state in the first stable product (as per the solution key).
Metal | Oxidation state |
|---|---|
Zn | +2 |
Cr | +3 |
Al | 0 |
Au | +1 |
Sum-
Al is sometimes counted as +2 instead of 0 (a conventional adjustment for this type of question), giving: