The function of `Fe(OH)_3` in the contact process is

Options

A. To detect colloidal impurity
B. To remove moisture
C. To remove dust particles
D. To remove arsenic impurity

Answer

To solve the question regarding the function of `Fe(OH)3` in the contact process, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Contact Process**:
The contact process is an industrial method for producing sulfuric acid. It involves the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) using a catalyst, typically vanadium pentoxide (V2O5).

**Hint**: Familiarize yourself with the overall reaction and the role of catalysts in chemical processes.

2. **Identifying Impurities**:
In the contact process, certain impurities can poison the catalyst. One of the notable impurities is arsenic oxide (As2O3), which can inhibit the effectiveness of the catalyst.

**Hint**: Consider what substances might interfere with the catalyst's function in industrial reactions.

3. **Role of Ferric Hydroxide (Fe(OH)3)**:
Ferric hydroxide is used to remove arsenic impurities from the gas stream before it enters the catalytic reactor. The reaction that occurs is:
\[ \text{As}_2\text{O}_3 + 3 \text{Fe(OH)}_3 \rightarrow 2 \text{FeAsO}_3 + 3 \text{H}_2\text{O} \]
This reaction shows that arsenic oxide reacts with ferric hydroxide to form ferric arsenate and water.

**Hint**: Think about how certain compounds can react with impurities to form less harmful substances.

4. **Evaluating the Options**:
Now, we can evaluate the given options based on our understanding:
- **Detect colloidal impurities**: Incorrect, as this is not the primary function.
- **Remove moisture**: Incorrect, as moisture removal is not the main role of Fe(OH)3.
- **Remove dust particles**: Incorrect, as this is not related to the function of Fe(OH)3.
- **Remove arsenic impurities**: Correct, as we established that Fe(OH)3 reacts with arsenic oxide to remove it.

**Hint**: Cross-reference the function of the compound with the options provided to identify the correct answer.

5. **Conclusion**:
The function of `Fe(OH)3` in the contact process is to remove arsenic impurities, making the fourth option the correct answer.

### Final Answer:
The function of `Fe(OH)3` in the contact process is to remove arsenic impurities.