Which of the following is not a Lewis acid?

Options

A. `AlCl_3`
B. `SnCl_4`
C. `FeCl_3`
D. `AlCl_3. 6H_2 O`

Answer

To determine which of the following is not a Lewis acid from the given options (AlCl3, SnCl4, FeCl3, AlCl3.6H2O), we need to understand the definition of a Lewis acid.

### Step-by-Step Solution:

1. **Understand the Definition of Lewis Acid**:
- A Lewis acid is defined as a species that can accept an electron pair from a Lewis base. This typically means that the Lewis acid has an empty orbital available to accommodate the incoming electron pair.

2. **Analyze Each Option**:
- **AlCl3**:
- Aluminum chloride (AlCl3) has an incomplete octet and can accept an electron pair, thus it acts as a Lewis acid.
- **SnCl4**:
- Tin(IV) chloride (SnCl4) also has an empty orbital and can accept electron pairs, making it a Lewis acid.
- **FeCl3**:
- Iron(III) chloride (FeCl3) can accept an electron pair as well, so it is also a Lewis acid.
- **AlCl3.6H2O**:
- Aluminum chloride hexahydrate (AlCl3.6H2O) has water molecules coordinated to the aluminum ion, which fills the coordination sphere and does not leave an empty orbital available for accepting electron pairs. Therefore, it does not act as a Lewis acid.

3. **Conclusion**:
- Among the options provided, **AlCl3.6H2O** is not a Lewis acid because it does not have an empty orbital available to accept an electron pair.

### Final Answer:
**AlCl3.6H2O** is not a Lewis acid.

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