Which of the following methods can be used for the preparation of anhydrous aluminium chloride

Options

A. heating `AlCl_(3)*6H_(2)O`
B. Heating a mixture of alumina and coke in a currennt of dry chlorine
C. Passing dry HCl gas over heated aluminium powder
D. Passing dry chlorine over heated aluminium

Answer

To determine which methods can be used for the preparation of anhydrous aluminum chloride (AlCl3), we will analyze each of the provided options step by step.

### Step 1: Analyze Option 1
**Option 1:** Heating AlCl3·6H2O

- When AlCl3·6H2O is heated, it loses water of crystallization. However, due to the covalent nature of AlCl3, it reacts with any residual water present to form aluminum hydroxide (Al(OH)3) instead of yielding anhydrous AlCl3.
- **Conclusion:** This method cannot be used to prepare anhydrous aluminum chloride.

### Step 2: Analyze Option 2
**Option 2:** Heating a mixture of alumina (Al2O3) and coke in a current of dry chlorine.

- The reaction can be represented as:
\[ \text{Al}_2\text{O}_3 + 3\text{C} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3 + 3\text{CO}_2 \]
- Here, alumina reacts with coke in the presence of dry chlorine to produce anhydrous AlCl3 and carbon dioxide (CO2).
- **Conclusion:** This method can be used to prepare anhydrous aluminum chloride.

### Step 3: Analyze Option 3
**Option 3:** Passing dry HCl gas over heated aluminum powder.

- The reaction can be represented as:
\[ 2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2 \]
- In this reaction, aluminum reacts with dry hydrochloric acid (HCl) to produce anhydrous AlCl3 and hydrogen gas (H2).
- **Conclusion:** This method can also be used to prepare anhydrous aluminum chloride.

### Step 4: Analyze Option 4
**Option 4:** Passing dry chlorine over heated aluminum.

- The reaction can be represented as:
\[ 2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3 \]
- Here, aluminum reacts directly with dry chlorine to produce anhydrous AlCl3.
- **Conclusion:** This method can be used to prepare anhydrous aluminum chloride.

### Final Conclusion
Based on the analysis:
- **Option 1** cannot be used to prepare anhydrous aluminum chloride.
- **Options 2, 3, and 4** can be used to prepare anhydrous aluminum chloride.

### Summary of Valid Methods
The valid methods for the preparation of anhydrous aluminum chloride are:
- Heating a mixture of alumina and coke in a current of dry chlorine (Option 2).
- Passing dry HCl gas over heated aluminum powder (Option 3).
- Passing dry chlorine over heated aluminum (Option 4).