Hydrogen gas will not reduce:

Options

A. heated cupric oxide
B. heated ferric oxide
C. heated stannic oxide
D. heated aluminium oxide

Answer

To determine which substance hydrogen gas will not reduce, we need to analyze the reduction potentials of the given compounds. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
The question involves four compounds:
1. Heated cupric oxide (CuO)
2. Heated ferric oxide (Fe2O3)
3. Heated stannous oxide (SnO2)
4. Heated aluminum oxide (Al2O3)

### Step 2: Determine Oxidation States
For each oxide, we need to determine the oxidation state of the metal:
- **CuO**: Copper (Cu) has an oxidation state of +2.
- **Fe2O3**: Iron (Fe) has an oxidation state of +3.
- **SnO2**: Tin (Sn) has an oxidation state of +4.
- **Al2O3**: Aluminum (Al) has an oxidation state of +3.

### Step 3: Write Reduction Reactions
Next, we write the reduction reactions for each metal ion:
1. **CuO**: Cu²⁺ + 2e⁻ → Cu
2. **Fe2O3**: 2Fe³⁺ + 6e⁻ → 2Fe²⁺
3. **SnO2**: Sn⁴⁺ + 2e⁻ → Sn²⁺
4. **Al2O3**: 2Al³⁺ + 6e⁻ → 2Al

### Step 4: Compare Electrode Potentials
To see if hydrogen can reduce these metal ions, we need to compare their standard electrode potentials (E°):
- **Fe³⁺/Fe²⁺**: E° = +0.77 V
- **Sn⁴⁺/Sn²⁺**: E° = +0.15 V
- **Cu²⁺/Cu**: E° = +0.34 V
- **Al³⁺/Al**: E° = -1.66 V

### Step 5: Analyze Reduction Ability
Hydrogen gas can only reduce metal ions that have a higher (more positive) standard electrode potential than itself (E° = 0 V).
- **Cu²⁺, Fe³⁺, and Sn⁴⁺** all have positive electrode potentials, meaning hydrogen can reduce these oxides.
- **Al³⁺** has a negative electrode potential, meaning hydrogen cannot reduce aluminum oxide.

### Conclusion
Thus, hydrogen gas will not reduce **heated aluminum oxide (Al2O3)**.

### Final Answer
**Heated aluminum oxide (Al2O3)** is the correct answer.

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