Balancing redox reactions can become quite complicated and a systematic approach should be used. The half-reaction method of balancing redox reactions emphasizes the fact that redox reactions can be separated into an oxidation half-reaction, which shows only the oxidation process and a reduction half-reactions which shows the reduction process. For the overall balanced reaction, the two half-reactions are combined so that the electrons in the two half-reactions cancel. The half-reaction method is particularly useful for reactions in aqueous solution. The two half-reactions are combined to make a balanced redox equation.
1. Which of the following represents a redox reaction?
- NaOH + HCl → NaCl + H2O
- BaCl2 + H2SO4 → BaSO4 + 2HCl
- CuSO4 + 2H2O → Cu(OH)2 + H2SO3
- Zn + 2HCl → ZnCl2 + H2
2. Which reaction involves neither oxidation nor reduction?
- CrO42- -→ Cr2O72-
- Cr → CrCl3
- Na → Na+
- 2S2O32- → S4O62-
3. Zn gives H2 gas with H2SO4 and HCl but not with HNO3 because
- Zn acts as an oxidising agent when it reacts with HNO3
- HNO3 is a weaker acid than H2SO4 and HCl
- In electrochemical series, Zn is above hydrogen
- NO3– is reduced in preference to hydronium ion
4. A compound of Xe and F is found to have 53.5% of Xe. What is the oxidation number of Xe in this compound?
5. A solution contains Fe2+, Fe3+ and I– ions. This solution was treated with iodine at 35oC. Eo for Fe3+/Fe2+ is 0.77V and Eo for I2/2I– = 0.536V. The favourable redox reaction is
- I2 will be reduced to I–
- there will be no redox reaction
- I– will be oxidised to I2
- Fe2+ will be oxidised to Fe3+
6. One mole of N2H4 loses 10 moles of electrons to form a new compound y. Assuming that all nitrogen appears in the new compound, what is the oxidation state of nitrogen in y.
7. The equivalent mass of oxidising agent in the following reaction is
SO2 + 2H2S → 3S + 2H2O
8. In the reaction
3Br2 + 6CO32- + 3H2O → 5Br– + BrO3– + 6HCO3–
- bromine is oxidised and carbonate is reduced
- bromine is reduced and water is oxidised
- bromine is neither reduced nor oxidised
- bromine is both reduced and oxidised
9. Which of the following cannot function as an oxidising agent?
10. The oxidation number of Pt in [Pt(C2H4)Cl3]– is