Concentated aqueous sodium hydroxide cannot separate a mixture of

Options

A. `Al^(3+)` and `Sn^(2+)`
B. `Al^(3+)` and `Fe^(3+)`
C. `Al^(3+)` and `Zn^(2+)`
D. `Zn^(3+)` and `Pb^(2+)`

Answer

To determine which mixture cannot be separated by concentrated aqueous sodium hydroxide (NaOH), we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the Mixtures:**
The question presents four pairs of cations:
- Option 1: Al³⁺ and Sn²⁺
- Option 2: Al³⁺ and Fe³⁺
- Option 3: Al³⁺ and Zn²⁺
- Option 4: Zn³⁺ and Pb²⁺

2. **Analyze Option 1: Al³⁺ and Sn²⁺**
- Al³⁺ reacts with NaOH to form sodium aluminate (NaAlO₂), which is soluble in NaOH.
- Sn²⁺ reacts with NaOH to form sodium stannate (Na₂SnO₂), which is also soluble in NaOH.
- **Conclusion:** Both are soluble, so they cannot be separated.

3. **Analyze Option 2: Al³⁺ and Fe³⁺**
- Al³⁺ forms sodium aluminate (NaAlO₂), which is soluble in NaOH.
- Fe³⁺ reacts with NaOH to form ferric hydroxide (Fe(OH)₃), which is insoluble in NaOH.
- **Conclusion:** This mixture can be separated because Fe³⁺ precipitates out.

4. **Analyze Option 3: Al³⁺ and Zn²⁺**
- Al³⁺ forms sodium aluminate (NaAlO₂), which is soluble in NaOH.
- Zn²⁺ reacts with NaOH to form sodium zincate (Na₂ZnO₂), which is also soluble in NaOH.
- **Conclusion:** Both are soluble, so they cannot be separated.

5. **Analyze Option 4: Zn³⁺ and Pb²⁺**
- Zn³⁺ reacts with NaOH to form sodium zincate (Na₂ZnO₂), which is soluble in NaOH.
- Pb²⁺ reacts with NaOH to form sodium plumbate (Na₂PbO₂), which is also soluble in NaOH.
- **Conclusion:** Both are soluble, so they cannot be separated.

### Final Conclusion:
The mixtures that cannot be separated by concentrated aqueous sodium hydroxide are:
- Option 1: Al³⁺ and Sn²⁺
- Option 3: Al³⁺ and Zn²⁺
- Option 4: Zn³⁺ and Pb²⁺

Thus, the correct answer is that concentrated aqueous sodium hydroxide cannot separate a mixture of **Al³⁺ and Sn²⁺, Al³⁺ and Zn²⁺, and Zn³⁺ and Pb²⁺**.